logger handles exception

src/fancymath/vector.py

@@ -16,8 +16,8 @@ class Vector(object):
     def dot(self, v):
         """Returns the dot product with Vector *v*."""
         if not isinstance(v, self.__class__):
-            logger.error(f"Expected an instance of {self.__class__}, but got {type(v)} instead.")
-            return None
+            msg = f"Expected an instance of {self.__class__}, but got {type(v)} instead."
+            raise ValueError(msg)
         d = self.x * v.x + self.y * v.y + self.z * v.z
         return d