This was noticed in Lithium-based yangtools.

For example:
enum "L-CSR-10M-APP-3Y=";

This will produce something like:

public enum VnfModel {
LCSR10MAPP3Y=(7),

Which java will obviously bark at (since it contains an equal sign. I know that RFC6020 suggests against using Unicode control codes, but "=" is not one so should be a valid character. A solution may be to replace "=" with a sentinel value in the compiled code?