The Service is setup in VuFind main module, the module does nothing
special except providing the classes and an autoloader configuration.

Thanks to Clemens Kynast and Michael Wiesen for development work.

Thanks to Arek Danszczyk and Christian Dabrowski.

Thanks to Nathan Tallman for help with development.

Includes integration test.

You introduced a new variable $query which doesn't exist. Changed it to $string as in the rest of the code.
Here it happened: https://github.com/dmj/vf2/commit/e6423f1f96c45411d4b42fce51ff41c20894aa22

Thanks to David Maus.