make validate_args() always return an array

see #883

diff --git a/php/WP_CLI/Dispatcher/Subcommand.php b/php/WP_CLI/Dispatcher/Subcommand.php
index 41b7a13..8f112c8 100644 (file)
--- a/php/WP_CLI/Dispatcher/Subcommand.php
+++ b/php/WP_CLI/Dispatcher/Subcommand.php
@@ -146,10 +146,13 @@ class Subcommand extends CompositeCommand {
                return array( $args, $assoc_args );
        }
 
+       /**
+        * @return array list of invalid $assoc_args keys to unset
+        */
        private function validate_args( $args, $assoc_args, $extra_args ) {
                $synopsis = $this->get_synopsis();
                if ( !$synopsis )
-                       return;
+                       return array();
 
                $validator = new \WP_CLI\SynopsisValidator( $synopsis );