SolrUtils::escapeQueryChars returns null if an empty string is passed in

[datadestroyd]

The following code:

<?php

var_dump(SolrUtils::escapeQueryChars(""));

Resulted in this output:

NULL

But I expected this output instead:

string(0) ""

The documentation states that the function will return the escaped string or false on failure. I don't think escaping an empty string should result in failure, but even if this was intended, the result should be false, not null.

Additionally, I would be like to know under what circumstances escaping even can fail. Maybe the documentation could give an example?