Our SAST shows possible NullPointerException in https://github.com/jruby/jruby/blob/master/core/src/main/java/org/jruby/runtime/ThreadContext.java#L937

    private RubyStackTraceElement[] getPartialTrace(int level, Integer length, Stream<StackWalker.StackFrame> stackStream) {
        if (length != null && length == 0) return RubyStackTraceElement.EMPTY_ARRAY;
        return TraceType.Gather.CALLER.getBacktraceData(this, stackStream).getPartialBacktrace(runtime, level + length);
    }

If length can be null, then it will cause NPE at level + length

Environment Information

We are analyzing versions 9.4.x (8-12), but this problem is still in master

Expected Behavior

• No NPE at all. But it seems nobody catch it through the years, so i don't know if this Integer may hold null at all

Actual Behavior

• have no tests to show this NPE, can't figure out how to make one. This is simply code analysis, that showed possible NPE