ENH: add imports that are needed for retrieving substructure

src/caosdb/utils/plantuml.py

@@ -36,6 +36,7 @@ plantuml FILENAME.pu -> FILENAME.png
 import os
 
 import caosdb as db
+from caosdb.common.datatype import is_reference, get_referenced_recordtype
 
 REFERENCE = "REFERENCE"