Fix bins input in get_zones (#1455)

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### Pull Request Checklist:
- [ ] This PR addresses an already opened issue (for bug fixes /
features)
    - This PR fixes #xyz
- [ ] Tests for the changes have been added (for bug fixes / features)
- [ ] (If applicable) Documentation has been added / updated (for bug
fixes / features)
- [x] CHANGES.rst has been updated (with summary of main changes)
- [x] Link to issue (:issue:`number`) and pull request (:pull:`number`)
has been added

### What kind of change does this PR introduce?

* Fix the condition that checks if `bins` is None or not. 

### Does this PR introduce a breaking change?
No

### Other information:

CHANGES.rst

@@ -4,7 +4,7 @@ Changelog
 
 v0.45.0 (unreleased)
 --------------------
-Contributors to this version: David Huard (:user:`huard`), Trevor James Smith (:user:`Zeitsperre`), Pascal Bourgault (:user:`aulemahal`), Juliette Lavoie (:user: `juliettelavoie`), Gabriel Rondeau-Genesse (:user:`RondeauG`), Marco Braun (:user:`vindelico`).
+Contributors to this version: David Huard (:user:`huard`), Trevor James Smith (:user:`Zeitsperre`), Pascal Bourgault (:user:`aulemahal`), Juliette Lavoie (:user:`juliettelavoie`), Gabriel Rondeau-Genesse (:user:`RondeauG`), Marco Braun (:user:`vindelico`), Éric Dupuis (:user:`coxipi`).
 
 New features and enhancements
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -21,6 +21,7 @@ Bug fixes
 * Fix `jetstream_metric_woollings` so it uses the `vertical` coordinate identified by `cf-xarray`, instead of `pressure`. (:issue:`1421`, :pull:`1422`). Add logic to handle coordinates in decreasing order, or for longitudes defined from 0-360 instead of -180 to 180. (:issue:`1429`, :pull:`1430`).
 * Fix virtual indicator attribute assignment causing individual indicator's realm to be ignored. (:issue:`1425`, :pull:`1426`).
 * Fixes the `raise_flags` argument of ``xclim.core.dataflags.data_flags`` so that an Exception is only raised when some checkups fail (:issue:`1456`, :pull:`1457`).
+* Fix ``xclim.indices.generic.get_zones`` so that `bins` can be given as input without error. (:pull:`1455`).
 
 Internal changes
 ^^^^^^^^^^^^^^^^

xclim/indices/generic.py

@@ -985,7 +985,7 @@ def get_zones(
         )
 
     # Get zone bins (if necessary)
-    bins = bins or _get_zone_bins(zone_min, zone_max, zone_step)
+    bins = bins if bins is not None else _get_zone_bins(zone_min, zone_max, zone_step)
     if isinstance(bins, list):
         bins = sorted([convert_units_to(b, da) for b in bins])
     else: