Trying to access array offset

ERROR:
	if ( is_array( $args[0] ) && isset( $_wp_theme_features['post-thumbnails'] ) ) {
				$args[0] = array_unique( array_merge( $_wp_theme_features['post-thumbnails'][0], $args[0] ) );
				return $args[0];
			}


FIX:

if ( isset( $args[0] ) && is_array( $args[0] ) && isset( $_wp_theme_features['post-thumbnails'] ) ) {
				$args[0] = array_unique( array_merge( $_wp_theme_features['post-thumbnails'][0], $args[0] ) );
			}