code: @Override
      public void visitEnd() {
          if (!fieldAlreadyExists) {
              FieldVisitor fv = super.visitField(
                                                 Opcodes.ACC_PUBLIC + Opcodes.ACC_FINAL + Opcodes.ACC_STATIC,
                                                 versionFieldName,
                                                 Type.getDescriptor(String.class),
                                                 null,
                                                 versionFieldValue);
              fv.visitEnd();
          }
  
          super.visitEnd();
      }
docs: End of class visitor that creates a version field definition if an
  existing definition wasn't observed.