Improve null response handling

Author: martinboulais

lib/server/gRPC/bindGRPCController.js

@@ -86,8 +86,8 @@ const adaptGrpcServiceMethodToControllerHandler = (
 
     const response = await controllerHandler(request);
 
-    if (!response) {
-        return response;
+    if (!(typeof response === 'object') || response === null) {
+        return null;
     }
 
     // Apply the gRPC converter to all the request parameters that needs it
@@ -129,8 +129,8 @@ const bindGRPCController = (serviceDefinition, implementation, absoluteMessagesD
             try {
                 const response = await adapter(call);
 
-                if (response === null || response === undefined) {
-                    callback(nativeToGRPCError(new Error(`Controller for ${path} returned a null response`)));
+                if (response === null) {
+                    callback(nativeToGRPCError(new Error(`Controller for ${path} returned an invalid response`)));
                 } else {
                     callback(null, response);
                 }