Make TypeBuilder.CreateType return non nullable

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/ModuleBuilder.cs

@@ -852,7 +852,7 @@ private void CreateGlobalFunctionsNoLock()
                 // cannot create globals twice
                 throw new InvalidOperationException(SR.InvalidOperation_NotADebugModule);
             }
-            _globalTypeBuilder.CreateType();
+            _globalTypeBuilder.CreateTypeImpl();
             _hasGlobalBeenCreated = true;
         }
 

src/coreclr/System.Private.CoreLib/src/System/Reflection/Emit/TypeBuilder.cs

@@ -694,6 +694,7 @@ private void SetGenParamCustomAttributeNoLock(CustAttr ca)
             m_ca ??= new List<TypeBuilder.CustAttr>();
             m_ca.Add(ca);
         }
+
         #endregion
 
         #region Object Overrides
@@ -1686,7 +1687,15 @@ private EventBuilder DefineEventNoLock(string name, EventAttributes attributes,
         }
 
         [return: DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
-        public Type? CreateType()
+        public Type CreateType()
+        {
+            Type? type = CreateTypeImpl();
+            Debug.Assert(type != null);
+            return type;
+        }
+
+        [return: DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)]
+        internal Type? CreateTypeImpl()
         {
             lock (SyncRoot)
             {

src/libraries/System.Reflection.Emit/ref/System.Reflection.Emit.cs

@@ -109,7 +109,7 @@ internal EnumBuilder() { }
         public System.Reflection.Emit.FieldBuilder UnderlyingField { get { throw null; } }
         public override System.Type UnderlyingSystemType { get { throw null; } }
         [return: System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
-        public System.Type? CreateType() { throw null; }
+        public System.Type CreateType() { throw null; }
         [return: System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.All)]
         public System.Reflection.TypeInfo? CreateTypeInfo() { throw null; }
         public System.Reflection.Emit.FieldBuilder DefineLiteral(string literalName, object? literalValue) { throw null; }

src/libraries/System.Reflection.Emit/tests/TypeBuilder/TypeBuilderCreateType.cs

@@ -28,6 +28,7 @@ public void CreateType(TypeAttributes attributes)
 
             TypeInfo typeInfo = type.CreateTypeInfo();
             Assert.Equal(typeInfo, createdType.GetTypeInfo());
+            Assert.NotNull(createdType);
 
             // Verify MetadataToken
             Assert.Equal(type.MetadataToken, typeInfo.MetadataToken);