SolidMaterial, MassProperties, VisualMaterial in Solid(..) and VisualMaterial in Visual(..) improved to handle corner cases:

- SolidMaterial=="" is treated as SolidMaterial = nothing
- VisualMaterial=="" is treated as Shapes.VisualMaterial()
- massProperties==nothing && solidMaterial==nothing is treated as MassProperties(), that is massless.

Author: MartinOtter

src/Composition/massPropertiesComputation.jl

@@ -104,7 +104,7 @@ function addOrSubtractMassPropertiesOfChildToRoot!(obj_root::Object3D{F}, obj_ch
         m = m_root + m_child
 
         # common center of mass (parent + child)
-        @assert(m > 0.0)
+        @assert(m >= 0.0)
         rCM = (m_root * rCM_root + m_child * rCM_child_new)/m
 
         # I: substract new common mass multiplied with skew matrices of

src/Shapes/massProperties.jl

@@ -15,7 +15,7 @@ struct MassProperties{F <: Modia3D.VarFloatType} <: Modia3D.AbstractMassProperti
     #---------------- different constructors for MassProperties -----------------
     # Constructor 0: takes mass, centerOfMass and inertiaMatrix as input values
     function MassProperties{F}(mass::Number, centerOfMass::AbstractVector, inertiaMatrix::AbstractMatrix) where F <: Modia3D.VarFloatType
-        @assert(mass > 0.0)
+        @assert(mass >= 0.0)
         new(mass, centerOfMass, inertiaMatrix)
     end
 end

src/Shapes/solid.jl

@@ -24,7 +24,7 @@ Generate a [Solid](@ref) with physical behavior of a rigid body with mass, visua
     computed from `shape` and `solidMaterial`. It is also possible to define only the mass of the solid and compute the
     center of mass and inertia tensor from `shape` (e.g. `MassPropertiesFromShapeAndMass(mass=4.5)`) or explicitly
     define all mass properties (e.g. `MassProperties(mass=4.5, centerOfMass=[1.0,2.0,3.0], Ixx=4.0, Iyy=5.0, Izz=6.0,
-    Ixy=4.5, Ixz=4.6, Iyz=5.5)`).
+    Ixy=4.5, Ixz=4.6, Iyz=5.5)`). 
 
 - `collision`: Defines if the solid is considered in [Collision Handling](@ref). `collision=true` requires definition
     of `shape`, mass properties (defined by `solidMaterial` or `massProperties`) and contact material (defined by
@@ -105,20 +105,25 @@ struct Solid{F <: Modia3D.VarFloatType} <: Modia3D.AbstractObject3DFeature
             contactMaterial = ""
         end
 
+        if typeof(solidMaterial) == String && solidMaterial == ""
+            solidMaterial = nothing
+        end
+        
         if typeof(solidMaterial) == String
             solidMaterial = solidMaterialPalette[1][solidMaterial]
         end
 
-        if typeof(visualMaterial) == String
-            visualMaterial = Shapes.visualMaterialPalette[visualMaterial]
+        if typeof(visualMaterial) == String 
+            visualMaterial = visualMaterial == "" ? Shapes.VisualMaterial() : Shapes.visualMaterialPalette[visualMaterial]
         end
 
         if typeof(shape) == FileMesh
             (shape.centroid, shape.shortestEdge, shape.longestEdge, shape.objPoints, shape.facesIndizes) = getMeshInfos(shape.filename, shape.scaleFactor)
             (shape.volume, shape.centroidAlgo, shape.inertia) = computeMassProperties(shape.objPoints, shape.facesIndizes; bodyCoords=false)
         end
 
-        massProperties = createMassProperties(F, massProperties, shape, solidMaterial)
+        massProperties = isnothing(massProperties) && isnothing(solidMaterial) ? MassProperties{F}() : createMassProperties(F, massProperties, shape, solidMaterial)
+
         contactSphereRadius::Union{Nothing,F} = isnothing(contactSphereRadius) || F(contactSphereRadius) <= F(0) ? nothing : F(contactSphereRadius)
         (isFlat, contactSphereRadius) = setContactSphereRadius(shape, contactSphereRadius, F)
         new(shape, solidMaterial, massProperties, collision, contactMaterial, setCollisionSmoothingRadius(shape, F(collisionSmoothingRadius)), visualMaterial, isFlat, contactSphereRadius)

src/Shapes/visual.jl

@@ -1,6 +1,7 @@
 convertStringToVisualMaterial(visualMaterial::Shapes.VisualMaterial) = visualMaterial
 
-convertStringToVisualMaterial(visualMaterial::AbstractString) = Shapes.visualMaterialPalette[visualMaterial]
+convertStringToVisualMaterial(visualMaterial::AbstractString) = visualMaterial == "" ? Shapes.VisualMaterial() : Shapes.visualMaterialPalette[visualMaterial]
+
 
 """
     Visual(;