function onWalk( error ) {
			if ( errFLG ) {
				return;
			}
			if ( error ) {
				debug( 'Encountered an error when walking file: %s (%d of %d). Error: %s', file, k, len, error.message );
				errFLG = true;
				return cb( error );
			}
			debug( 'Successfully walked file: %s (%d of %d).', file, k, len );

			count += 1;
			debug( 'Walked %d of %d files.', count, len );
			if ( count === len ) {
				return cb( null, toArray( cache ) );
			}
		}
Callback invoked upon walking a file.

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