Fix indexing NaT scalars

xray/core/variable.py

@@ -149,7 +149,15 @@ def __getitem__(self, key):
             key, = key
 
         if isinstance(key, (int, np.integer)):
-            value = np.asarray(self.array[key], dtype=self.dtype)
+            value = self.array[key]
+            if value is pd.NaT:
+                # work around the impossibility of casting NaT with asarray
+                # note: it probably would be better in general to return
+                # pd.Timestamp rather np.than datetime64 but this is easier
+                # (for now)
+                value = np.datetime64('NaT', 'ns')
+            else:
+                value = np.asarray(value, dtype=self.dtype)
         else:
             arr = self.array[key]
             if arr.dtype != self.array.dtype:

xray/test/test_variable.py

@@ -90,6 +90,11 @@ def test_index_0d_datetime(self):
         x = self.cls(['x'], pd.DatetimeIndex([d]))
         self.assertIndexedLikeNDArray(x, np.datetime64(d), 'datetime64[ns]')
 
+    def test_index_0d_not_a_time(self):
+        d = np.datetime64('NaT')
+        x = self.cls(['x'], [d])
+        self.assertIndexedLikeNDArray(x, d, None)
+
     def test_index_0d_object(self):
 
         class HashableItemWrapper(object):