TraceurException.appendTo crashes app

[kassim]

So your code in TraceurException is

    public Throwable appendTo(Throwable throwable) {
        Throwable t = throwable;
        while (t.getCause() != null) {
            t = t.getCause();

            // Won't be able to init the cause of this with self
            if (t == this) {
                return throwable;
            }

            if (logLevel == LogLevel.SHOW_ONLY_FIRST && t instanceof TraceurException) {
                return throwable;
            }
        }

        t.initCause(this);

        return throwable;
    }

but the code inside Throwable is

    public synchronized Throwable initCause(Throwable cause) {
        if (this.cause != this)
            throw new IllegalStateException("Can't overwrite cause with " +
                                            Objects.toString(cause, "a null"), this);
        if (cause == this)
            throw new IllegalArgumentException("Self-causation not permitted", this);
        this.cause = cause;
        return this;
    }

This means the appendTo function will cause an exception to be thrown if a Throwable's cause is ever found to be null.

Possible solution
while (t.getCause() != null) should be while (t.getCause() != null && t.getCause() != t) and wrap the t.initCause(this);with a check againstt.getCause()`'s nullability

I'll make a PR later with this