message: make NodeH implicitly cast to bool
diff: @@ -116,6 +116,9 @@ namespace ospray {
  NodeH operator[] (const std::string &c) const
  { return node->child(c); }
  + NodeH operator[] (const char *c) const
  + { return node->child(c); }
  +
  //! add child node n to this node
  NodeH operator+= (NodeH n)
  { get()->add(n); n->setParent(*this); return n;}
  @@ -127,6 +130,8 @@ namespace ospray {
  //! is this handle pointing to a null value?
  bool isNULL() const { return node.get() == nullptr; }
  + operator bool() const { return !isNULL(); }
  +
  // Data members //
  std::shared_ptr<sg::Node> node;
  