function done( error, results ) {
		if ( error ) {
			return cb( error );
		}
		debug( 'Finished analysis.' );
		if ( results ) {
			return cb( null, results );
		}
		if ( opts.cumulative ) {
			return cb( null, null );
		}
		return cb( null, [] );
	}
Callback invoked upon completion.

@private
@param {(Error|null)} error - error object
@param {(Object|ArrayArray)} results - analysis results
@returns {void}