Update wizards.compare_publications to add protections

controllers/wizards.py

@@ -15,7 +15,8 @@ from plugin_dbui import (CALLBACK_ERRORS,
                          is_foreign_field,
                          JSONEncoder,
                          Selector,
-                         to_fields)
+                         to_fields,
+                         UNDEF_ID)
 
 MODE_DRY_RUN = T(DRY_RUN)
 MSG_NO_AUTHORS = "<br><br>Removing affiliation failed.<br>"\
@@ -238,6 +239,10 @@ def compare_publications():
         if is_foreign_field(field):
             k_tablename, k_fieldname, k_id = get_foreign_field(field)
 
+            # protection against None
+            value1 = (UNDEF_ID if value1 is None else value1)
+            value2 = (UNDEF_ID if value2 is None else value2)
+
             value1 = db[k_tablename][value1][k_fieldname]
             value2 = db[k_tablename][value2][k_fieldname]