fix: missing return when converting to frequency

toargridding/metadata.py

@@ -37,7 +37,7 @@ class TimeSample:
 
     @property
     def frequency(self):
-        TIME_FREQUENCIES[self.sampling]
+        return TIME_FREQUENCIES[self.sampling]
 
     def as_cf_index(self):
         n_days = (self.end - self.start).days