Python : Make sure an empty list will be received as empty list

See https://github.com/OPM/ResInsight/issues/8508
Python code linting changes detected by black

GrpcInterface/Python/rips/pdmobject.py

@@ -223,6 +223,9 @@ class PdmObjectBase:
     def __makelist(self, list_string):
         list_string = list_string.lstrip("[")
         list_string = list_string.rstrip("]")
+        if not list_string:
+            # Return empty list if empty string. Otherwise, the split function will return ['']
+            return []
         strings = list_string.split(", ")
         values = []
         for string in strings:

GrpcInterface/Python/rips/tests/test_summary_cases.py

@@ -109,6 +109,7 @@ def test_summary_no_unsmry(rips_instance, initialize_test):
         summary_case = rips_instance.project.import_summary_case(temp_path)
         assert summary_case is None
 
+
 def test_summary_set_values(rips_instance, initialize_test):
     casePath = dataroot.PATH + "/flow_diagnostics_test/SIMPLE_SUMMARY2.SMSPEC"
     summary_case = rips_instance.project.import_summary_case(casePath)