Fix URL for RequireExplicitNullMarking checker

nullaway/src/main/java/com/uber/nullaway/RequireExplicitNullMarking.java

@@ -73,4 +73,9 @@ private static boolean hasNullMarkedOrNullUnmarkedAnnotation(Symbol symbol) {
     return ASTHelpers.hasDirectAnnotationWithSimpleName(symbol, "NullMarked")
         || ASTHelpers.hasDirectAnnotationWithSimpleName(symbol, "NullUnmarked");
   }
+
+  @Override
+  public String linkUrl() {
+    return "https://github.com/uber/NullAway/wiki/JSpecify-Support#requireexplicitnullmarking-checker ";
+  }
 }

nullaway/src/test/java/com/uber/nullaway/RequireExplicitNullMarkingTest.java

@@ -35,6 +35,18 @@ public void missingNullMarkedAnnotationOnTopLevelClass() {
         .doTest();
   }
 
+  @Test
+  public void defaultURL() {
+    compilationHelper
+        .addSourceLines(
+            "test/MissingAnnotation.java",
+            "package test;",
+            "// BUG: Diagnostic contains: https://github.com/uber/NullAway/wiki/JSpecify-Support#requireexplicitnullmarking-checker",
+            "class MissingAnnotation {",
+            "}")
+        .doTest();
+  }
+
   /** Test that at SUGGESTION level, no report is made for missing annotations */
   @Test
   public void noReportAtDefaultLevel() {