code: public static void addFallbackInputMap(Node node, InputMap<?> im) {
          // getInputMap calls init, so can use unsafe setter
          setInputMapUnsafe(node, InputMap.sequence(getInputMap(node), im));
      }
docs: Adds the given input map to the end of the node's list of input maps, so that an event will be pattern-matched
  against all other input maps currently "installed" in the node before being pattern-matched against the given
  input map.