Fix bug with empty endpoint (#744)

src/sakia/data/entities/node.py

@@ -10,11 +10,14 @@ def _tuple_of_endpoints(value):
         l = [endpoint(e) for e in value]
         return tuple(l)
     elif isinstance(value, str):
+        if value:
             list_of_str = value.split('\n')
             conv = []
             for s in list_of_str:
                 conv.append(endpoint(s))
             return conv
+        else:
+            return []
     else:
         raise TypeError("Can't convert {0} to list of endpoints".format(value))