Validation Package Testing

- Added More Unit Tests to Validation Classes
- Updated Logic accordingly

lib/PayPal/Validation/ArgumentValidator.php

@@ -16,18 +16,17 @@ class ArgumentValidator
      * @param $argument     mixed The object to be validated
      * @param $argumentName string|null The name of the argument.
      *                      This will be placed in the exception message for easy reference
+     * @return bool
      */
     public static function validate($argument, $argumentName = null)
     {
-        if (
-            $argument != null &&
-            ((gettype($argument) == 'string' && $argument == '') || is_array($argument) && empty($argument))
-        ) {
-            //Throw an Exception for string or array
-            throw new \InvalidArgumentException("$argumentName cannot be null or empty");
-        } elseif ($argument === null) {
-            //Generic Exception
+        if ($argument === null) {
+            // Error if Object Null
             throw new \InvalidArgumentException("$argumentName cannot be null");
+        } else if (gettype($argument) == 'string' && trim($argument) == ''){
+            // Error if String Empty
+            throw new \InvalidArgumentException("$argumentName string cannot be empty");
         }
+        return true;
     }
 }