Minor bug fix for tests.WarningChecker when IERS is down

CHANGELOG.md

@@ -50,6 +50,9 @@ fully tested and didn't work properly.
 - Having `freq_array` and `channel_width` defined on wide-band UVCal objects.
 
 ### Fixed
+- A small bug (mostly affecting continuous integration) that threw an error when the
+IERS service was down and when tests were using `test.check_warnings` to look for no
+warnings thrown (i.e., where `match=None`).
 - A couple of small bugs related to handling of the `freq_range` parameter in the
 `reorder_freqs` and `__add__` methods on `UVCal`.
 

pyuvdata/tests/__init__.py

@@ -126,11 +126,12 @@ def __enter__(self):
             warnings.filterwarnings("ignore", message="time is out of IERS range")
 
             test_message = []
-            for message in self.match:
-                if message is None:
-                    test_message.append(False)
-                else:
-                    test_message.append(message.startswith("LST values stored in "))
+            if self.match is not None:
+                for message in self.match:
+                    if message is None:
+                        test_message.append(False)
+                    else:
+                        test_message.append(message.startswith("LST values stored in "))
             if not any(test_message):
                 warnings.filterwarnings("ignore", message="LST values stored in ")