diff --git a/src/caoscrawler/converters/converters.py b/src/caoscrawler/converters/converters.py
index 69fb76006123a62d0b672caf1f2be13265d5a8d1..61ab4545c7c9ad3e34882f3030ca63c9b20a2d6b 100644
--- a/src/caoscrawler/converters/converters.py
+++ b/src/caoscrawler/converters/converters.py
@@ -636,7 +636,7 @@ class Converter(object, metaclass=ABCMeta):
                 tr_func = transformer_functions[tr_func_key]
                 # Call the function:
                 sig = signature(tr_func)
-                if len(sig.parameters) == 1 and tr_func_params:
+                if len(sig.parameters) == 1 and not tr_func_params:  # FIXME Test for this line.
                     out_value = tr_func(in_value)
                 else:
                     out_value = tr_func(in_value, tr_func_params)