core/src/main/java/com/twitter/elephantbird/util/Protobufs.java
public static List<String> getMessageFieldNames(Class<? extends Message> protoClass, Map<String, String> fieldNameTranslations) {
    return getMessageFieldNames(getMessageDescriptor(protoClass), fieldNameTranslations);
  }
public static List<String> getMessageFieldNames(Class<? extends Message> protoClass, Map<String, String> fieldNameTranslations) {
    return getMessageFieldNames(getMessageDescriptor(protoClass), fieldNameTranslations);
  }
{ "a" => "A", "c" => "IGNORE" }, then you'll end up with A, b