ENH: Better error message.

src/caosadvancedtools/json_schema_exporter.py

@@ -259,7 +259,8 @@ class JsonSchemaExporter:
             A dict containing the json schema created from the given RecordType's properties.
         """
         if rt is None:
-            raise ValueError("`rt` must not be None.")
+            raise ValueError(
+                "recordtype_to_json_schema(...) cannot be called with a `None` RecordType.")
         schema = self._make_segment_from_recordtype(rt)
         schema["$schema"] = "https://json-schema.org/draft/2019-09/schema"
         if rt.name: