diff --git a/py/string_function.py b/py/string_function.py
index fa56674..532e974 100644
--- a/py/string_function.py
+++ b/py/string_function.py
@@ -21,6 +21,14 @@ class StringFunction:
     OUTPUT_NODE = True
 
     def exec(self, action, tidy_tags, text_a, text_b, text_c=""):
+        # Converted inputs are sent as the string of 'undefined' if not connected
+        if text_a == "undefined":
+            text_a = ""
+        if text_b == "undefined":
+            text_b = ""
+        if text_c == "undefined":
+            text_c = ""
+            
         tidy_tags = tidy_tags == "yes"
         out = ""
         if action == "append":