code: private boolean doTryInsertNoLock(S storable) {
          // Create a fresh copy to ensure that custom fields are not saved.
          S copy = (S) storable.prepare();
          storable.copyAllProperties(copy);
          copy.markAllPropertiesClean();
          Key<S> key = new Key<S>(copy, mFullComparator);
          S existing = mMap.get(key);
          if (existing != null) {
              return false;
          }
          mMap.put(key, copy);
          storable.markAllPropertiesClean();
          return true;
      }
docs: Caller must hold upgrade or write lock.