diff --git a/docs/pyerrors/obs.html b/docs/pyerrors/obs.html
index 7da0c303..2e3aab18 100644
--- a/docs/pyerrors/obs.html
+++ b/docs/pyerrors/obs.html
@@ -1292,7 +1292,10 @@
new_names.append(name)
new_deltas[name] = np.array(nd)
new_idl[name] = ni
- return (new_names, new_deltas, new_idl)
+ if new_names:
+ return (new_names, new_deltas, new_idl)
+ else:
+ return (names, deltas, idl)
def derived_observable(func, data, **kwargs):