refactor: add non-negativity check for plant scaling values

powersimdata/input/change_table.py

@@ -190,6 +190,7 @@ def _add_plant_entries(self, resource, ct_key, zone_name=None, plant_id=None):
             load zone(s).
         :param dict plant_id: identification numbers of plants. The key(s) is
             (are) the id of the plant(s).
+        :raise ValueError: if any values within zone_name or plant_id are negative.
         """
         self._check_resource(resource)
         if bool(zone_name) or bool(plant_id) is True:
@@ -201,6 +202,8 @@ def _add_plant_entries(self, resource, ct_key, zone_name=None, plant_id=None):
                 except ValueError:
                     self.ct.pop(ct_key)
                     raise
+                if not all([v >= 0 for v in zone_name.values()]):
+                    raise ValueError(f"All entries for {ct_key} must be non-negative")
                 if "zone_id" not in self.ct[ct_key]:
                     self.ct[ct_key]["zone_id"] = {}
                 for z in zone_name.keys():