address feedback

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/BaseNumberConverter.cs

@@ -49,7 +49,7 @@ public override bool CanConvertFrom(ITypeDescriptorContext? context, Type source
         /// <summary>
         /// Converts the given value object to an object of Type TargetType.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string text)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/BooleanConverter.cs

@@ -25,7 +25,7 @@ public override bool CanConvertFrom(ITypeDescriptorContext? context, Type source
         /// Converts the given value
         /// object to a Boolean object.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string text)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/CharConverter.cs

@@ -39,7 +39,7 @@ public override bool CanConvertFrom(ITypeDescriptorContext? context, Type source
         /// <summary>
         /// Converts the given object to a Unicode character object.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string text)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/CollectionChangeEventArgs.cs

@@ -25,6 +25,6 @@ public CollectionChangeEventArgs(CollectionChangeAction action, object? element)
         /// <summary>
         /// Gets the instance of the collection with the change.
         /// </summary>
-        public virtual object? Element { get; } // TODO-NULLABLE: System.Data.Common doesn't seem to expect this to be null but we do not guard against it
+        public virtual object? Element { get; }
     }
 }

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/CultureInfoConverter.cs

@@ -61,7 +61,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
         /// Converts the specified value object to a <see cref='System.Globalization.CultureInfo'/>
         /// object.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             // Only when GetCultureName returns culture.Name, we use CultureInfoMapper
             // (Since CultureInfoMapper will transfer Culture.DisplayName to Culture.Name).

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/DateTimeConverter.cs

@@ -35,7 +35,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
         /// <summary>
         /// Converts the given value object to a <see cref='System.DateTime'/> object.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string text)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/DateTimeOffsetConverter.cs

@@ -35,7 +35,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
         /// Converts the given value object to a <see cref='System.DateTime'/>
         /// object.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string text)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/Design/PropertyTabAttribute.cs

@@ -153,7 +153,6 @@ public override bool Equals([NotNullWhen(true)] object? other)
             return false;
         }
 
-        // TODO-NULLABLE: other should most likely be nullable but will throw NRE
         public bool Equals(PropertyTabAttribute other)
         {
             if (other == (object)this)

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/EnumConverter.cs

@@ -72,7 +72,7 @@ private static long GetEnumValue(bool isUnderlyingTypeUInt64, Enum enumVal, Cult
         /// <summary>
         /// Converts the specified value object to an enumeration object.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string strValue)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/GuidConverter.cs

@@ -35,7 +35,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
         /// <summary>
         /// Converts the given object to a globally unique identifier object.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string text)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/NullableConverter.cs

@@ -246,7 +246,7 @@ public override bool GetStandardValuesSupported(ITypeDescriptorContext? context)
         /// <summary>
         /// Gets a value indicating whether the given value object is valid for this type.
         /// </summary>
-        public override bool IsValid(ITypeDescriptorContext? context, object? value)
+        public override bool IsValid(ITypeDescriptorContext? context, object value)
         {
             if (UnderlyingTypeConverter != null)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/PropertyDescriptorCollection.cs

@@ -6,7 +6,6 @@
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 
-// TODO-NULLABLE: This class needs more attention. Many APIs allow null properties but some other don't expect it (i.e. Find).
 namespace System.ComponentModel
 {
     /// <summary>
@@ -21,7 +20,7 @@ public class PropertyDescriptorCollection : ICollection, IList, IDictionary
 
         private IDictionary? _cachedFoundProperties;
         private bool _cachedIgnoreCase;
-        private PropertyDescriptor?[] _properties;
+        private PropertyDescriptor[] _properties;
         private readonly string[]? _namedSort;
         private readonly IComparer? _comparer;
         private bool _propsOwned;
@@ -58,7 +57,7 @@ public PropertyDescriptorCollection(PropertyDescriptor[]? properties, bool readO
             _readOnly = readOnly;
         }
 
-        private PropertyDescriptorCollection(PropertyDescriptor?[] properties, int propCount, string[]? namedSort, IComparer? comparer)
+        private PropertyDescriptorCollection(PropertyDescriptor[] properties, int propCount, string[]? namedSort, IComparer? comparer)
         {
             _propsOwned = false;
             if (namedSort != null)
@@ -208,7 +207,7 @@ private void EnsureSize(int sizeNeeded)
                 {
                     if (ignoreCase)
                     {
-                        if (string.Equals(_properties[i]!.Name, name, StringComparison.OrdinalIgnoreCase))
+                        if (string.Equals(_properties[i].Name, name, StringComparison.OrdinalIgnoreCase))
                         {
                             _cachedFoundProperties[name] = _properties[i];
                             p = _properties[i];
@@ -217,7 +216,7 @@ private void EnsureSize(int sizeNeeded)
                     }
                     else
                     {
-                        if (_properties[i]!.Name.Equals(name))
+                        if (_properties[i].Name.Equals(name))
                         {
                             _cachedFoundProperties[name] = _properties[i];
                             p = _properties[i];
@@ -274,7 +273,7 @@ public void RemoveAt(int index)
             {
                 Array.Copy(_properties, index + 1, _properties, index, Count - index - 1);
             }
-            _properties[Count - 1] = null;
+            _properties[Count - 1] = null!;
             Count--;
         }
 
@@ -292,7 +291,7 @@ public virtual PropertyDescriptorCollection Sort()
         /// Sorts the members of this PropertyDescriptorCollection. Any specified NamedSort arguments will
         /// be applied first, followed by sort using the specified IComparer.
         /// </summary>
-        public virtual PropertyDescriptorCollection Sort(string[] names)
+        public virtual PropertyDescriptorCollection Sort(string[]? names)
         {
             return new PropertyDescriptorCollection(_properties, Count, names, _comparer);
         }
@@ -301,7 +300,7 @@ public virtual PropertyDescriptorCollection Sort(string[] names)
         /// Sorts the members of this PropertyDescriptorCollection. Any specified NamedSort arguments will
         /// be applied first, followed by sort using the specified IComparer.
         /// </summary>
-        public virtual PropertyDescriptorCollection Sort(string[] names, IComparer comparer)
+        public virtual PropertyDescriptorCollection Sort(string[]? names, IComparer? comparer)
         {
             return new PropertyDescriptorCollection(_properties, Count, names, comparer);
         }
@@ -310,7 +309,7 @@ public virtual PropertyDescriptorCollection Sort(string[] names, IComparer compa
         /// Sorts the members of this PropertyDescriptorCollection, using the specified IComparer to compare,
         /// the PropertyDescriptors contained in the collection.
         /// </summary>
-        public virtual PropertyDescriptorCollection Sort(IComparer comparer)
+        public virtual PropertyDescriptorCollection Sort(IComparer? comparer)
         {
             return new PropertyDescriptorCollection(_properties, Count, _namedSort, comparer);
         }
@@ -361,7 +360,7 @@ protected void InternalSort(string[]? names)
                 {
                     if (propList[i] != null)
                     {
-                        _properties[foundCount++] = propList[i];
+                        _properties[foundCount++] = propList[i]!;
                     }
                 }
 

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ProvidePropertyAttribute.cs

@@ -24,7 +24,7 @@ public ProvidePropertyAttribute(
             }
 
             PropertyName = propertyName;
-            ReceiverTypeName = receiverType.AssemblyQualifiedName!; // TODO-NULLABLE: ReceiverTypeName should be guarded against nulls
+            ReceiverTypeName = receiverType.AssemblyQualifiedName!;
         }
 
         /// <summary>

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/ReferenceConverter.cs

@@ -43,7 +43,7 @@ public override bool CanConvertFrom(ITypeDescriptorContext? context, Type source
         /// <summary>
         /// Converts the given object to the reference type.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string text)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TimeSpanConverter.cs

@@ -36,7 +36,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
         /// Converts the given object to a <see cref='System.TimeSpan'/>
         /// object.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string text)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeConverter.cs

@@ -46,12 +46,12 @@ public virtual bool CanConvertTo(ITypeDescriptorContext? context, Type? destinat
         /// <summary>
         /// Converts the given value to the converter's native type.
         /// </summary>
-        public object? ConvertFrom(object? value) => ConvertFrom(null, CultureInfo.CurrentCulture, value);
+        public object? ConvertFrom(object value) => ConvertFrom(null, CultureInfo.CurrentCulture, value);
 
         /// <summary>
         /// Converts the given object to the converter's native type.
         /// </summary>
-        public virtual object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public virtual object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is InstanceDescriptor instanceDescriptor)
             {
@@ -79,7 +79,7 @@ public virtual bool CanConvertTo(ITypeDescriptorContext? context, Type? destinat
         /// <summary>
         /// Converts the specified text into an object.
         /// </summary>
-        public object? ConvertFromString(string? text) => ConvertFrom(null, null, text);
+        public object? ConvertFromString(string text) => ConvertFrom(null, null, text);
 
         /// <summary>
         /// Converts the specified text into an object.
@@ -92,7 +92,7 @@ public virtual bool CanConvertTo(ITypeDescriptorContext? context, Type? destinat
         /// <summary>
         /// Converts the specified text into an object.
         /// </summary>
-        public object? ConvertFromString(ITypeDescriptorContext? context, CultureInfo? culture, string? text)
+        public object? ConvertFromString(ITypeDescriptorContext? context, CultureInfo? culture, string text)
         {
             return ConvertFrom(context, culture, text);
         }
@@ -307,7 +307,7 @@ protected Exception GetConvertToException(object? value, Type destinationType)
         /// <summary>
         /// Gets a value indicating whether the given value object is valid for this type.
         /// </summary>
-        public virtual bool IsValid(ITypeDescriptorContext? context, object? value)
+        public virtual bool IsValid(ITypeDescriptorContext? context, object value)
         {
             bool isValid = true;
             try
@@ -317,7 +317,7 @@ public virtual bool IsValid(ITypeDescriptorContext? context, object? value)
                 // NullableConverter would consider null value as a valid value.
                 if (value == null || CanConvertFrom(context, value.GetType()))
                 {
-                    ConvertFrom(context, CultureInfo.InvariantCulture, value);
+                    ConvertFrom(context, CultureInfo.InvariantCulture, value!);
                 }
                 else
                 {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeDescriptor.cs

@@ -1027,7 +1027,6 @@ public static EventDescriptorCollection GetEvents(
                 return new EventDescriptorCollection(null, true);
             }
 
-            // TODO-NULLABLE: Investigate if NRE can actually happen and if we should handle it
             return GetDescriptor(componentType, nameof(componentType))!.GetEvents();
         }
 
@@ -1046,7 +1045,6 @@ public static EventDescriptorCollection GetEvents(
                 return new EventDescriptorCollection(null, true);
             }
 
-            // TODO-NULLABLE: Investigate if NRE can actually happen and if we should handle it
             EventDescriptorCollection events = GetDescriptor(componentType, nameof(componentType))!.GetEvents(attributes);
 
             if (attributes != null && attributes.Length > 0)
@@ -1260,7 +1258,6 @@ public static PropertyDescriptorCollection GetProperties(
                 return new PropertyDescriptorCollection(null, true);
             }
 
-            // TODO-NULLABLE: Investigate if NRE can actually happen and if we should handle it
             return GetDescriptor(componentType, nameof(componentType))!.GetProperties();
         }
 
@@ -1279,7 +1276,6 @@ public static PropertyDescriptorCollection GetProperties(
                 return new PropertyDescriptorCollection(null, true);
             }
 
-            // TODO-NULLABLE: Investigate if NRE can actually happen and if we should handle it
             PropertyDescriptorCollection properties = GetDescriptor(componentType, nameof(componentType))!.GetProperties(attributes);
 
             if (attributes != null && attributes.Length > 0)
@@ -2694,7 +2690,6 @@ internal ComNativeDescriptionProvider(IComNativeDescriptorHandler handler)
 
                 if (instance == null)
                 {
-                    // TODO-NULLABLE: If this returned new EmptyCustomTypeDescriptor() then base class's return value could likely be not null
                     return null;
                 }
 

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/TypeListConverter.cs

@@ -45,7 +45,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
         /// <summary>
         /// Converts the specified value object to an enumeration object.
         /// </summary>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/ComponentModel/VersionConverter.cs

@@ -36,7 +36,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
         ///    <para>Converts the given object to a Version.</para>
         /// </summary>
         /// <exception cref="FormatException"><paramref name="value"/> is not a valid version string</exception>
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string versionString)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/Drawing/ColorConverter.cs

@@ -35,7 +35,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
             return destinationType == typeof(InstanceDescriptor) || base.CanConvertTo(context, destinationType);
         }
 
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string strValue)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/Drawing/PointConverter.cs

@@ -22,7 +22,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
             return destinationType == typeof(InstanceDescriptor) || base.CanConvertTo(context, destinationType);
         }
 
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string strValue)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/Drawing/RectangleConverter.cs

@@ -22,7 +22,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
             return destinationType == typeof(InstanceDescriptor) || base.CanConvertTo(context, destinationType);
         }
 
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string strValue)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/Drawing/SizeConverter.cs

@@ -22,7 +22,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
             return destinationType == typeof(InstanceDescriptor) || base.CanConvertTo(context, destinationType);
         }
 
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string strValue)
             {

src/libraries/System.ComponentModel.TypeConverter/src/System/Drawing/SizeFConverter.cs

@@ -22,7 +22,7 @@ public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destina
             return destinationType == typeof(InstanceDescriptor) || base.CanConvertTo(context, destinationType);
         }
 
-        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object? value)
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
         {
             if (value is string strValue)
             {