function done( error ) {
		if ( clbk.length === 2 ) {
			if ( error ) {
				return clbk( error, false );
			}
			return clbk( null, true );
		}
		if ( error ) {
			return clbk( false );
		}
		return clbk( true );
	}
Callback invoked upon performing a filesystem call.

@private
@param {(Error|null)} error - error object
@returns {void}