code: public GinjectorBindings getInstallPosition(Key<?> key) {
      Preconditions.checkNotNull(positions,
          "Must call position before calling getInstallPosition(Key<?>)");
      GinjectorBindings position = installOverrides.get(key);
      if (position == null) {
        position = positions.get(key);
      }
      return position;
    }
docs: Returns the Ginjector where the binding for key should be placed, or null if the key was
  removed from the dependency graph earlier.