fixed empty iterator console output error (StopIteration)

pym/calculate/lib/utils/tools.py

@@ -195,7 +195,6 @@ class SingletonParam(type):
             cls.instance[keyarg] = create_obj(*args, **kw)
         return cls.instance[keyarg]
 
-
 def classificate(iterator):
     """
     Классифицировать элементы по признаку (first первый last последний)
@@ -209,8 +208,13 @@ def classificate(iterator):
         def __repr__(self):
             return "Mark(first=%s,last=%s)" % (self.first, self.last)
 
+
     iterator = iter(iterator)
-    obj = next(iterator)
+    try:
+        obj = next(iterator)
+    except StopIteration:
+        #empty iterator
+        return
     try:
         obj_next = next(iterator)
         yield Mark(first=True, last=False), obj