Your change works fine and solves this issue. With the debugger I can see it now skips the body of the if ( isJavaFxInClasspath() ) code.

Because I don't know/have the time to properly download and build Hibernate Validator from scratch, I have tested this in this way:

• turned off my workaround
• downloaded the modified LoadClass.java and ConfigurationImpl.java and put them into the Eclipse plugin that embeds hibernate-validator-5.2.1.Final.jar and exports it's packages
• run my application and verified with the debugger that these versions of the classes are used, instead of those inside the jar, that the error is gone and the code using Hibernate Validator runs fine now
• removed the java files, running the application again and verifying that the error I reported is back