Merge pull request #439 from sosswald/fix-428

Fix crash of rqt_graph when enable_statistics == true, fixes #428

rqt_graph/src/rqt_graph/dotcode.py

@@ -172,7 +172,7 @@ def _calc_statistic_info(self, sub, topic, pub=None):
         if pub is None and sub in self.edges and topic in self.edges[sub]:
             conns = len(self.edges[sub][topic])
             if conns == 1:
-                pub = next(self.edges[sub][topic].keys())
+                pub = next(iter(self.edges[sub][topic].keys()))
             else:
                 penwidth = self._calc_edge_penwidth(sub,topic)
                 color = self._calc_edge_color(sub,topic)