[ticket/16955] Fix most return types in phpdoc

PHPBB3-16955

phpBB/includes/diff/diff.php

@@ -544,7 +544,7 @@ class diff3 extends diff
 	* @param string $label2 the cvs file version/label from the new set of lines
 	* @param string $label_sep the explanation between label1 and label2 - more of a helper for the user
 	*
-	* @return mixed the merged output
+	* @return array the merged output
 	*/
 	function get_conflicts_content($label1 = 'CURRENT_FILE', $label2 = 'NEW_FILE', $label_sep = 'DIFF_SEP_EXPLAIN')
 	{
@@ -582,7 +582,7 @@ class diff3 extends diff
 	/**
 	* Return merged output (used by the renderer)
 	*
-	* @return mixed the merged output
+	* @return array the merged output
 	*/
 	function merged_output()
 	{

phpBB/includes/diff/renderer.php

@@ -793,7 +793,7 @@ class diff_renderer_side_by_side extends diff_renderer
 	{
 		if ($this->state == 'empty')
 		{
-			return '';
+			return;
 		}
 
 		// This is just an addition line.