chunked Median does not work
**Description**
The stats median node reduced _chunk method does not work.

**Steps to Reproduce**
```
coords = Coordinate(
    lat=(0, 1, 10),
    lon=(0, 1, 10),
    time=('2018-01-01', '2018-01-10', '1,D'),
    order=['lat', 'lon', 'time'])

a = np.random.random(coords.shape)
source = NumpyArray(source=a, native_coordinates=coords)
data = source.execute(coords)
node = Median(source=source)

output = node.execute(coords)
output_chunked = node.execute(coords, {'iter_chunk_size': 100})
```

**Expected Behavior**
The reduce and reduce_chunked should both work and should return the same output.

**Observed Behavior**
The chunked execution raises an Exception.

**Additional Notes**
There is a failing testing for this that is currently flagged to skip.

diff --git a/podpac/core/algorithm/stats.py b/podpac/core/algorithm/stats.py
index d0df1be1..580d6540 100644
--- a/podpac/core/algorithm/stats.py
+++ b/podpac/core/algorithm/stats.py
@@ -869,9 +869,12 @@ class Reduce2(Reduce):
         UnitsDataArray
             Reduced output.
         """
-        I = [self.input_coordinates.dims.index(dim)
-             for dim in
-             self.evaluated_coordinates.dims]
+        # special case for full reduce
+        if not self.evaluated_coordinates.dims:
+            xslc, x = next(xs)
+            return self.reduce(x)
+
+        I = [self.input_coordinates.dims.index(dim) for dim in self.evaluated_coordinates.dims]
         y = xr.full_like(self.output, np.nan)
         for xslc, x in xs:
             yslc = [xslc[i] for i in I]
diff --git a/podpac/core/algorithm/test/test_stats.py b/podpac/core/algorithm/test/test_stats.py
index 27ebdd0a..7845380f 100644
--- a/podpac/core/algorithm/test/test_stats.py
+++ b/podpac/core/algorithm/test/test_stats.py
@@ -167,7 +167,6 @@ class TestKurtosis(BaseTests):
     def setup_class(cls):
         cls.node = Kurtosis(source=source)
 
-@pytest.mark.skip("not-yet-working")
 class TestMedian(BaseTests):
     @classmethod
     def setup_class(cls):
['podpac/core/algorithm/test/test_stats.py', 'podpac/core/algorithm/stats.py']