prevent `Compilation.GetSymbolsWithName() from returning null entries

src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs

@@ -2940,7 +2940,11 @@ public IEnumerable<ISymbol> GetSymbolsWithName(Func<string, bool> predicate, Sym
                     if (includeNamespace && predicate(current.Name))
                     {
                         var container = GetSpineSymbol(spine);
-                        set.Add(GetSymbol(container, current));
+                        var symbol = GetSymbol(container, current);
+                        if (symbol != null)
+                        {
+                            set.Add(symbol);
+                        }
                     }
                 }
                 else
@@ -2948,7 +2952,11 @@ public IEnumerable<ISymbol> GetSymbolsWithName(Func<string, bool> predicate, Sym
                     if (includeType && predicate(current.Name))
                     {
                         var container = GetSpineSymbol(spine);
-                        set.Add(GetSymbol(container, current));
+                        var symbol = GetSymbol(container, current);
+                        if (symbol != null)
+                        {
+                            set.Add(symbol);
+                        }
                     }
 
                     if (includeMember)
@@ -2984,13 +2992,16 @@ public IEnumerable<ISymbol> GetSymbolsWithName(Func<string, bool> predicate, Sym
                 spine.Add(current);
 
                 var container = GetSpineSymbol(spine);
-                foreach (var member in container.GetMembers())
+                if (container != null)
                 {
-                    if (!member.IsTypeOrTypeAlias() &&
-                        (member.CanBeReferencedByName || member.IsExplicitInterfaceImplementation() || member.IsIndexer()) &&
-                        predicate(member.Name))
+                    foreach (var member in container.GetMembers())
                     {
-                        set.Add(member);
+                        if (!member.IsTypeOrTypeAlias() &&
+                            (member.CanBeReferencedByName || member.IsExplicitInterfaceImplementation() || member.IsIndexer()) &&
+                            predicate(member.Name))
+                        {
+                            set.Add(member);
+                        }
                     }
                 }
 

src/Compilers/VisualBasic/Portable/Compilation/VisualBasicCompilation.vb

@@ -2681,12 +2681,18 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                 If current.Kind = DeclarationKind.Namespace Then
                     If includeNamespace AndAlso predicate(current.Name) Then
                         Dim container = GetSpineSymbol(spine)
-                        [set].Add(GetSymbol(container, current))
+                        Dim symbol = GetSymbol(container, current)
+                        If symbol IsNot Nothing Then
+                            [set].Add(symbol)
+                        End If
                     End If
                 Else
                     If includeType AndAlso predicate(current.Name) Then
                         Dim container = GetSpineSymbol(spine)
-                        [set].Add(GetSymbol(container, current))
+                        Dim symbol = GetSymbol(container, current)
+                        If symbol IsNot Nothing Then
+                            [set].Add(symbol)
+                        End If
                     End If
 
                     If includeMember Then
@@ -2719,7 +2725,9 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                 For Each name In mergedType.MemberNames
                     If predicate(name) Then
                         container = If(container, GetSpineSymbol(spine))
-                        [set].UnionWith(container.GetMembers(name))
+                        If container IsNot Nothing Then
+                            [set].UnionWith(container.GetMembers(name))
+                        End If
                     End If
                 Next