Let _active_result_class be NULL by default

In this case, asynchronous method calls will return NULL themselves.

Cython/Compiler/ModuleNode.py

@@ -1055,7 +1055,8 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 templates_code = "template <typename %s>" % ", typename ".join(t.name for t in entry.type.templates)
                 code.putln(templates_code)
             code.putln("%s {" % function_code)
-            code.putln("%s = this->%s();" % (result_interface_type.declaration_code("result_object"), result_attr_cname))
+            result_declaration = result_interface_type.declaration_code("result_object")
+            code.putln("%s = this->%s ? this->%s() : NULL;" % (result_declaration, result_attr_cname, result_attr_cname))
 
             message_constructor_args_list = ["this", "sync_object", "result_object"] + reified_arg_cname_list
             message_constructor_args_code = ", ".join(message_constructor_args_list)
@@ -1196,12 +1197,14 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             )
 
             if does_return:
+                code.putln("if (this->%s != NULL) {" % result_attr_cname)
                 code.putln("Cy_WLOCK(this->%s);" % result_attr_cname)
                 if reified_function_entry.type.return_type.resolve() is PyrexTypes.c_int_type:
                     code.putln("this->%s->pushIntResult(result);" % result_attr_cname)
                 else:
                     code.putln("this->%s->pushVoidStarResult((void*)result);" % result_attr_cname)
                 code.putln("Cy_UNWLOCK(this->%s);" % result_attr_cname)
+                code.putln("}")
             code.putln("return 1;")
             code.putln("}")
 

Cython/Utility/CyObjects.cpp

@@ -390,7 +390,7 @@
 
         struct ActhonActivableClass : public CyObject {
             ActhonQueueInterface *_active_queue_class = NULL;
-            ActhonResultInterface *(*_active_result_class)(void);
+            ActhonResultInterface *(*_active_result_class)(void) = NULL;
             ActhonActivableClass(){} // Used in Activated classes inheritance chain (base Activated calls this, derived calls the 2 args version below)
             virtual ~ActhonActivableClass();
         };