Fix bug in meta patch STDIN detection

Author: schlessera

src/WP_CLI/CommandWithMeta.php

@@ -4,6 +4,7 @@
 
 use WP_CLI;
 use WP_CLI\Entity\RecursiveDataStructureTraverser;
+use WP_CLI\Entity\Utils as EntityUtils;
 
 /**
  * Base class for WP-CLI commands that deal with metadata
@@ -396,12 +397,13 @@ public function patch( $args, $assoc_args ) {
 
 		if ( 'delete' == $action ) {
 			$patch_value = null;
-		} elseif ( Entity\Utils::has_stdin() ) {
-			$stdin_value = WP_CLI::get_value_from_arg_or_stdin( $args, -1 );
-			$patch_value = WP_CLI::read_value( trim( $stdin_value ), $assoc_args );
 		} else {
-			// Take the patch value as the last positional argument. Mutates $key_path to be 1 element shorter!
-			$patch_value = WP_CLI::read_value( array_pop( $key_path ), $assoc_args );
+			$stdin_value = EntityUtils::has_stdin()
+				? trim( WP_CLI::get_value_from_arg_or_stdin( $args, -1 ) )
+				: null;
+			$patch_value = ! empty( $stdin_value )
+				? WP_CLI::read_value( $stdin_value, $assoc_args )
+				: WP_CLI::read_value( array_pop( $key_path ), $assoc_args );
 		}
 
 		/* Need to make a copy of $current_meta_value here as it is modified by reference */