API/FIX : don't accept None for x or y in plot

This addresses #4339 by preventing it.

lib/matplotlib/axes/_base.py

@@ -263,6 +263,14 @@ def _plot_args(self, tup, kwargs):
             raise ValueError('third arg must be a format string')
         else:
             linestyle, marker, color = None, None, None
+
+        # check that n values of None are passed in
+        # this will be upconverted to a one element array
+        # of None, which will cause problems later when
+        # we try to draw.
+        if any(v is None for v in tup):
+            raise ValueError("x and y must not be None")
+
         kw = {}
         for k, v in zip(('linestyle', 'marker', 'color'),
                         (linestyle, marker, color)):