Fix a possible NRE in XmlDocumentationElement and wrong nullable annotations in analyzers.

ICSharpCode.Decompiler/Documentation/XmlDocumentationElement.cs

@@ -193,9 +193,9 @@ namespace ICSharpCode.Decompiler.Documentation
 							if (inheritedFrom != null)
 								inheritedDocumentation = "<doc>" + inheritedFrom.GetDocumentation() + "</doc>";
 						}
-						else
+						else if (declaringEntity != null)
 						{
-							foreach (IMember baseMember in InheritanceHelper.GetBaseMembers((IMember?)declaringEntity, includeImplementedInterfaces: true))
+							foreach (IMember baseMember in InheritanceHelper.GetBaseMembers((IMember)declaringEntity, includeImplementedInterfaces: true))
 							{
 								inheritedDocumentation = baseMember.GetDocumentation();
 								if (inheritedDocumentation != null)

ICSharpCode.ILSpyX/Analyzers/Builtin/MethodUsedByAnalyzer.cs

@@ -45,7 +45,7 @@ namespace ICSharpCode.ILSpyX.Analyzers.Builtin
 			Debug.Assert(analyzedSymbol is IMethod);
 
 			var analyzedMethod = (IMethod)analyzedSymbol;
-			var analyzedBaseMethod = (IMethod)InheritanceHelper.GetBaseMember(analyzedMethod);
+			var analyzedBaseMethod = (IMethod?)InheritanceHelper.GetBaseMember(analyzedMethod);
 			if (analyzedMethod.ParentModule?.MetadataFile == null)
 				yield break;
 			var mapping = context.Language
@@ -109,12 +109,12 @@ namespace ICSharpCode.ILSpyX.Analyzers.Builtin
 			}
 		}
 
-		bool IsUsedInMethod(IMethod analyzedEntity, IMethod analyzedBaseMethod, IMethod method, AnalyzerContext context)
+		bool IsUsedInMethod(IMethod analyzedEntity, IMethod? analyzedBaseMethod, IMethod method, AnalyzerContext context)
 		{
 			return ScanMethodBody(analyzedEntity, method, analyzedBaseMethod, context.GetMethodBody(method));
 		}
 
-		static bool ScanMethodBody(IMethod analyzedMethod, IMethod method, IMethod analyzedBaseMethod, MethodBodyBlock? methodBody)
+		static bool ScanMethodBody(IMethod analyzedMethod, IMethod method, IMethod? analyzedBaseMethod, MethodBodyBlock? methodBody)
 		{
 			if (methodBody == null || method.ParentModule?.MetadataFile == null)
 				return false;