If a value to convert doesn't have units, just return

dstansby · dstansby · commit 5dcab5e32c5b · 2018-01-09T20:22:40.000Z
diff --git a/lib/matplotlib/axis.py b/lib/matplotlib/axis.py
@@ -1498,6 +1498,10 @@ def have_units(self):
         return self.converter is not None or self.units is not None
 
     def convert_units(self, x):
+        # If x is already a number, doesn't need converting
+        if munits.ConversionInterface.is_numlike(x):
+            return x
+
         if self.converter is None:
             self.converter = munits.registry.get_converter(x)
 
diff --git a/lib/matplotlib/dates.py b/lib/matplotlib/dates.py
@@ -1738,8 +1738,6 @@ def convert(value, unit, axis):
 
         The *unit* and *axis* arguments are not used.
         """
-        if units.ConversionInterface.is_numlike(value):
-            return value
         return date2num(value)
 
     @staticmethod
