requires_fit is not all available all the time

bob/pipelines/mixins.py

@@ -245,7 +245,7 @@ class SampleMixin(BaseEstimator):
         # See: https://scikit-learn.org/stable/developers/develop.html
         # if the estimator does not require fit or is stateless don't call fit
         tags = self._get_tags()
-        if tags["stateless"] or not tags["requires_fit"]:
+        if tags["stateless"] or ("requires_fit" in tags and not tags["requires_fit"]):
             return self
 
         # if the estimator needs to be fitted.