Source

File: wp-includes/class-walker-nav-menu.php

public function end_lvl( &$output, $depth = 0, $args = null ) {
		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {
			$t = '';
			$n = '';
		} else {
			$t = "\t";
			$n = "\n";
		}
		$indent  = str_repeat( $t, $depth );
		$output .= "$indent</ul>{$n}";
	}