There is a bug JBEAP-12968. It was very hard to find out was is going on as stacktrace of exception was hidden. Even setting TRACE level in jboss-cli.properties does not reveal anything.

 ./jboss-cli.bat -c "-Dwildfly.config.url=C:\wildfly-config.xml"
java.lang.ExceptionInInitializerError: java.lang.NullPointerException

Please log full stacktrace.

This issue is meant as general exception handling (logging) from static methods of ClientConfiguration e.g. getInstance() [1].

[1] https://github.com/rstancel/wildfly-client-config/blob/ffee8f5f1fd6aa33385828547312882687dd2a03/src/main/java/org/wildfly/client/config/ClientConfiguration.java#L223