code: public String getCanonicalID() {
          if (canonicalID == null) {
              synchronized(this) {
                  if (canonicalID == null) {
                      canonicalID = getCanonicalID(getID());
  
                      assert(canonicalID != null);
                      if (canonicalID == null) {
                          // This should never happen...
                          canonicalID = getID();
                      }
                  }
              }
          }
          return canonicalID;
      }
docs: Returns the canonical ID of this system time zone