function clbk( error, bool ) {
		if ( error ) {
			return done( error );
		}
		if ( bool ) {
			return done( null, x );
		}
		done( null, y );
	}
Callback invoked by a predicate function.

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