private static int compareHandlesNulls(CstString a, CstString b) {
    if (a == b) {
      return 0;
    } else if (a == null) {
      return -1;
    } else if (b == null) {
      return 1;
    } else {
      return a.compareTo(b);
    }
  }
Compares two strings like String.compareTo(), excepts treats a null as the least-possible
string value.

@return negative integer, zero, or positive integer in accordance with Comparable.compareTo()
android/android_framework/dex-maker/src/main/java/com/android/dx/rop/code/LocalItem.java