added additional internal string helpers for missing/invalid args

lib/internals.js

@@ -70,6 +70,20 @@ export default {
       return `Missing required argument of type '${type}' for method '${method}()'.`;
     },
 
+    /**
+     * @return {string}
+     */
+    ERROR_MISSING_ARG_NAMED(name, type, method) {
+      return `Missing required argument '${name}' of type '${type}' for method '${method}()'.`;
+    },
+
+    /**
+     * @return {string}
+     */
+    ERROR_ARG_INVALID_VALUE(name, expected, got) {
+      return `Invalid value for argument '${name}' expected value '${expected}' but got '${got}'.`;
+    },
+
     /**
      * @return {string}
      */