Source

File: wp-includes/class-wp-object-cache.php

public function add( $key, $data, $group = 'default', $expire = 0 ) {
		if ( wp_suspend_cache_addition() ) {
			return false;
		}

		if ( empty( $group ) ) {
			$group = 'default';
		}

		$id = $key;
		if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) ) {
			$id = $this->blog_prefix . $key;
		}

		if ( $this->_exists( $id, $group ) ) {
			return false;
		}

		return $this->set( $key, $data, $group, (int) $expire );
	}