get_substitutions: fix empty keyword error

models/redner_template.py

@@ -434,7 +434,7 @@
         for name in varlist:
             while "." in name:
                 name = name[: name.rfind(".")]
-                if name not in varlist:
+                if name not in varlist and name != "":
                     varlist.append(name)
 
         varlist.sort()