private static String getStackTraceString(Throwable tr) {
    if (tr == null) {
      return "";
    }
    return Log.getStackTraceString(tr);
  }
Note: this gets forwarded to {@code android.util.Log.e} as {@code android.util.Log.wtf} might
crash the app.
fbcore/src/main/java/com/facebook/common/logging/FLogDefaultLoggingDelegate.java