allow one of the eval points to be None

theano/tensor/basic.py

@@ -4556,11 +4556,12 @@ class Dot(Op):
     def R_op(self, inputs, eval_points):
         # R_op for a \dot b evaluted at c for a and d for b is
         # simply c \dot b + a \dot d
-        if None in eval_points:
-            return [None]
+
 
         assert len(inputs) == 2
         assert len(eval_points) == 2
+        if eval_points[0] is None and eval_points[1] is None:
+            return [None]
 
         debugger_available = config.compute_test_value != 'off'
 
@@ -4605,11 +4606,17 @@ class Dot(Op):
                                      ' %s and %s, respectively' % (
                             str(input_values[i].shape),
                             str(eval_point_values[i].shape)))
-
-        t1 = self(eval_points[0], inputs[1])
-        t2 = self(inputs[0], eval_points[1])
-
-        return [t1 + t2]
+        if eval_points[0]:
+            t1 = self(eval_points[0], inputs[1])
+        if eval_points[1]:
+            t2 = self(inputs[0], eval_points[1])
+
+        if eval_points[0] and eval_points[1]:
+            return [t1 + t2]
+        elif eval_points[0]:
+            return [t1]
+        else:
+            return [t2]
 
     def infer_shape(self, node, shapes):
         xshp, yshp = shapes