QOL Update for Masking

Author: AstroPatty

opencosmo/dataset/index.py

@@ -345,7 +345,7 @@ def mask(self, mask: np.ndarray) -> DataIndex:
             raise ValueError(f"Mask dtype {mask.dtype} is not boolean")
 
         if not mask.any():
-            raise ValueError("Mask is all False")
+            raise EmptyMaskError("Mask is all False")
 
         if mask.all():
             return self