[JavaLangStringBuilder isEmpty]: unrecognized selector sent to instance

[zbynek]

Running transpiled code like this

StringBuilder sb = new StringBuilder();
if (sb.isEmpty()) {
  sb.append("");
}

I get

[JavaLangStringBuilder isEmpty]: unrecognized selector sent to instance

using self-compiled j2objc version 7e76bfd.
The default implementation is present at that commit: https://github.com/google/j2objc/blame/7e76bfd/jre_emul/android/platform/libcore/ojluni/src/main/java/java/lang/CharSequence.java#L89
so I'm not sure where the problem is.