Custom method can now have nullable parameters and nullable arguments

src/Microsoft.AspNetCore.OData/Query/Expressions/ExpressionBinderBase.cs

@@ -688,7 +688,7 @@ private Expression BindEndsWith(SingleValueFunctionCallNode node)
 
             Contract.Assert(arguments.Length == 2 && arguments[0].Type == typeof(string) && arguments[1].Type == typeof(string));
 
-            return ExpressionBinderHelper.MakeFunctionCall(ClrCanonicalFunctions.EndsWith, QuerySettings, arguments);
+            return ExpressionBinderHelper.MakeCustomFunctionCall(ClrCanonicalFunctions.EndsWith, arguments);
         }
 
         private Expression BindCustomMethodExpressionOrNull(SingleValueFunctionCallNode node)

src/Microsoft.AspNetCore.OData/Query/Expressions/ExpressionBinderHelper.cs

@@ -249,6 +249,22 @@ public static Expression MakeFunctionCall(MemberInfo member, ODataQuerySettings
             return CreateFunctionCallWithNullPropagation(functionCall, arguments, querySettings);
         }
 
+        //Custom methods might contain nullable parameters and, therefore, also should be able to take arguments of type Nullable<T>
+        public static Expression MakeCustomFunctionCall(MethodInfo method, params Expression[] arguments)
+        {
+            Expression functionCall;
+            if (method.IsStatic)
+            {
+                functionCall = Expression.Call(null, method, arguments);
+            }
+            else
+            {
+                functionCall = Expression.Call(arguments.First(), method, arguments.Skip(1));
+            }
+
+            return functionCall;
+        }
+
         public static Expression CreateFunctionCallWithNullPropagation(Expression functionCall, Expression[] arguments, ODataQuerySettings querySettings)
         {
             if (querySettings.HandleNullPropagation == HandleNullPropagationOption.True)

src/Microsoft.AspNetCore.OData/Query/Expressions/QueryBinder.SingleValueFunctionCall.cs

@@ -761,7 +761,7 @@ protected virtual Expression BindCustomMethodExpressionOrNull(SingleValueFunctio
             MethodInfo methodInfo;
             if (UriFunctionsBinder.TryGetMethodInfo(node.Name, methodArgumentsType, out methodInfo))
             {
-                return ExpressionBinderHelper.MakeFunctionCall(methodInfo, context.QuerySettings, arguments);
+                return ExpressionBinderHelper.MakeCustomFunctionCall(methodInfo, arguments);
             }
 
             return null;