Fix error editing prop templates with None PrimaryMeasureType

E.g. all qto props have it's None

Error traceback:
Error: Python: Traceback (most recent call last):
  File "\bonsai\bim\module\pset_template\operator.py", line 135, in execute
    props.active_prop_template.primary_measure_type = template.PrimaryMeasureType
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: bpy_struct: item.attr = val: expected a string enum, not NoneType

src/bonsai/bonsai/bim/module/pset_template/data.py

@@ -58,10 +58,12 @@ class PsetTemplatesData:
             return []
         schema = ifcopenshell.ifcopenshell_wrapper.schema_by_name(ifc_file.schema)
         version = ifc_file.schema
-        return [
+        enum_items = [
             (t, t, ifcopenshell.util.doc.get_type_doc(version, t).get("description", ""))
             for t in sorted([d.name() for d in schema.declarations() if hasattr(d, "declared_type")])
         ]
+        enum_items = [("-", "-", "")] + enum_items
+        return enum_items
 
     @classmethod
     def property_template_type(cls) -> list[tuple[str, str, str]]:

src/bonsai/bonsai/bim/module/pset_template/operator.py

@@ -132,7 +132,7 @@ class EnableEditingPropTemplate(bpy.types.Operator):
         template = IfcStore.pset_template_file.by_id(props.active_prop_template_id)
         props.active_prop_template.name = template.Name or ""
         props.active_prop_template.description = template.Description or ""
-        props.active_prop_template.primary_measure_type = template.PrimaryMeasureType
+        props.active_prop_template.primary_measure_type = template.PrimaryMeasureType or "-"
         props.active_prop_template.template_type = template.TemplateType
         props.active_prop_template.enum_values.clear()
 
@@ -287,13 +287,18 @@ class EditPropTemplate(bpy.types.Operator, tool.PsetTemplate.PsetTemplateOperato
     bl_options = {"REGISTER", "UNDO"}
 
     def _execute(self, context):
+        assert IfcStore.pset_template_file
         props = context.scene.BIMPsetTemplateProperties
+        active_prop_template = props.active_prop_template
         if props.active_prop_template.template_type == "P_ENUMERATEDVALUE":
             data_type = props.active_prop_template.get_value_name()
             prop = props.active_prop_template
             enumerators = [getattr(ev, data_type) for ev in prop.enum_values]
         else:
             enumerators = None
+        if (primary_measure_type := active_prop_template.primary_measure_type) == "-":
+            primary_measure_type = None
+
         ifcopenshell.api.run(
             "pset_template.edit_prop_template",
             IfcStore.pset_template_file,
@@ -301,7 +306,7 @@ class EditPropTemplate(bpy.types.Operator, tool.PsetTemplate.PsetTemplateOperato
             attributes={
                 "Name": props.active_prop_template.name,
                 "Description": props.active_prop_template.description,
-                "PrimaryMeasureType": props.active_prop_template.primary_measure_type,
+                "PrimaryMeasureType": primary_measure_type,
                 "TemplateType": props.active_prop_template.template_type,
                 "Enumerators": enumerators,
             },