Improvement required by issue #102. Error message and docstring conta…

…ins more details and removed unnecessary line of code

pyhaystack/client/session.py

@@ -239,9 +239,8 @@ def point_write(
         the writeable point entity to retrieve the write status of or write a
         value to.
 
-        If level is None, the other parameters are required to be None too, the
-        write status of the point is retrieved.  Otherwise, a write is
-        performed to the nominated point.
+        To retrieve the write status of the point, value, duration and level are required to be None.
+        To write to a point, value and level are required and duration is optional.
         """
         who = who or self._username
         return self._on_point_write(
@@ -523,10 +522,9 @@ def _on_watch_poll(self, watch, refresh, callback, **kwargs):
     def _on_point_write(self, point, level, val, who, duration, callback, **kwargs):
         args = {"id": self._obj_to_ref(point)}
         if level is None:
-            who = None  # as it may be username
             if (val is not None) or (duration is not None):
                 raise ValueError(
-                    "If level is None, val, who and duration must " "be None too."
+                    "You tried writing a value without specifying a level (or specified a duration without providing a level neither a value. Please provide required level. If trying to retrieve write status of the point, provide None as value, duration and level"
                 )
         else:
             args.update({"level": level, "val": val})