FIX(scanner): variables are only replaced if parameters are present at all

src/caoscrawler/converters/converters.py

@@ -583,6 +583,7 @@ class Converter(object, metaclass=ABCMeta):
                     raise RuntimeError("Unknown transformer function: {}".format(tr_func_key))
 
                 # Do variable replacment on function parameters:
+                if tr_func_params is not None:
                     for key in tr_func_params:
                         tr_func_params[key] = replace_variables(tr_func_params[key], values)