Only use climo_subsections if it is non-empty (#804)

Default is climo_subsections="", so if it was not defined in the input
configuration, the climo_subsections param would exist, but be empty
and the subsections would not be infered.

Author: mkstratos

zppy/livvkit.py

@@ -131,7 +131,7 @@ def determine_and_add_dependencies(
     )
 
     climo_subsections: List[str] = []
-    if "climo_subsections" in _c.keys():
+    if ("climo_subsections" in _c.keys()) and _c["climo_subsections"]:
         climo_subsections = _c["climo_subsections"]
     elif ("infer_section_parameters" in _c.keys()) and _c["infer_section_parameters"]:
         grids = ["_native"]