REF: Error if some optimization variable is passed no values

Author: kernc

backtesting/backtesting.py

@@ -1235,6 +1235,11 @@ def constraint(_):
         def _tuple(x):
             return x if isinstance(x, Sequence) and not isinstance(x, str) else (x,)
 
+        for k, v in kwargs.items():
+            if len(_tuple(v)) == 0:
+                raise ValueError("Optimization variable '{0}' is passed no "
+                                 "optimization values: {0}={1}".format(k, v))
+
         class AttrDict(dict):
             def __getattr__(self, item):
                 return self[item]

backtesting/test/_test.py

@@ -507,6 +507,7 @@ def test_multiprocessing_windows_spawn(self):
     def test_optimize_invalid_param(self):
         bt = Backtest(GOOG.iloc[:100], SmaCross)
         self.assertRaises(AttributeError, bt.optimize, foo=range(3))
+        self.assertRaises(ValueError, bt.optimize, fast=[])
 
     def test_optimize_no_trades(self):
         bt = Backtest(GOOG, SmaCross)