diff --git a/py/string_function.py b/py/string_function.py
index 10069fe..12ea3de 100644
--- a/py/string_function.py
+++ b/py/string_function.py
@@ -1,100 +1,123 @@
-import re
-
-class StringFunction:
-    @classmethod
-    def INPUT_TYPES(s):
-        return {
-            "required": {
-                "action": (["append", "replace"], {}),
-                "tidy_tags": (["yes", "no"], {}),
-            },
-            "optional": {
-                "text_a": ("STRING", {"multiline": True}),
-                "text_b": ("STRING", {"multiline": True}),
-                "text_c": ("STRING", {"multiline": True}),
-                "text_d": ("STRING", {"multiline": True}),
-                "text_e": ("STRING", {"multiline": True}),
-                "text_f": ("STRING", {"multiline": True}),
-                "text_g": ("STRING", {"multiline": True}),
-                "text_h": ("STRING", {"multiline": True}),
-                "text_i": ("STRING", {"multiline": True}),
-                "text_j": ("STRING", {"multiline": True}),
-                "text_k": ("STRING", {"multiline": True}),
-                "text_l": ("STRING", {"multiline": True}),
-                "text_m": ("STRING", {"multiline": True}),
-                "text_n": ("STRING", {"multiline": True}),
-                "text_o": ("STRING", {"multiline": True}),
-                "text_p": ("STRING", {"multiline": True}),
-                "text_q": ("STRING", {"multiline": True}),
-                "text_r": ("STRING", {"multiline": True}),
-            }
-        }
-
-    RETURN_TYPES = ("STRING",)
-    FUNCTION = "exec"
-    CATEGORY = "utils"
-    OUTPUT_NODE = True
-
-    def exec(self, action, tidy_tags, text_a="", text_b="", text_c="", text_d="", text_e="", text_f="", text_g="", text_h="",
-             text_i="", text_j="", text_k="", text_l="", text_m="", text_n="", text_o="", text_p="", text_q="", text_r=""):
-        # Converted inputs are sent as the string of 'undefined' if not connected
-        if text_a == "":
-            text_a = ""
-        if text_b == "":
-            text_b = ""
-        if text_c == "":
-            text_c = ""
-        if text_d == "":
-            text_d = ""
-        if text_e == "":
-            text_e = ""
-        if text_f == "":
-            text_f = ""
-        if text_g == "":
-            text_g = ""
-        if text_h == "":
-            text_h = ""
-        if text_i == "":
-            text_i = ""
-        if text_j == "":
-            text_j = ""
-        if text_k == "":
-            text_k = ""
-        if text_l == "":
-            text_l = ""
-        if text_m == "":
-            text_m = ""
-        if text_n == "":
-            text_n = ""
-        if text_o == "":
-            text_o = ""
-        if text_p == "":
-            text_p = ""
-        if text_q == "":
-            text_q = ""
-        if text_r == "":
-            text_r = ""
-
-        tidy_tags = tidy_tags == "yes"
-        out = ""
-        if action == "append":
-            out = (", " if tidy_tags else "").join(filter(None, [text_a, text_b, text_c, text_d, text_e, text_f, text_g, text_h, text_i, text_j, text_k, text_l, text_m, text_n, text_o, text_p, text_q, text_r]))
-        else:
-            if text_r is None:
-                text_r = ""
-            if text_b.startswith("/") and text_b.endswith("/"):
-                regex = text_b[1:-1]
-                out = re.sub(regex, text_r, text_a)
-            else:
-                out = text_a.replace(text_b, text_r)
-        if tidy_tags:
-            out = out.replace("  ", " ").replace(" ,", ",").replace(",,", ",").replace(",,", ",")
-        return {"ui": {"text": (out,)}, "result": (out,)}
-
-NODE_CLASS_MAPPINGS = {
-    "StringFunction": StringFunction,
-}
-
-NODE_DISPLAY_NAME_MAPPINGS = {
-    "StringFunction": "String Function Tree",
-}
+import re
+
+class StringFunction:
+    @classmethod
+    def INPUT_TYPES(s):
+        return {
+            "required": {
+                "action": (["append", "replace"], {}),
+                "tidy_tags": (["yes", "no"], {}),
+            },
+            "optional": {
+                "text_a": ("STRING", {"multiline": True}),
+                "text_b": ("STRING", {"multiline": True}),
+                "text_c": ("STRING", {"multiline": True}),
+                "text_d": ("STRING", {"multiline": True}),
+                "text_e": ("STRING", {"multiline": True}),
+                "text_f": ("STRING", {"multiline": True}),
+                "text_g": ("STRING", {"multiline": True}),
+                "text_h": ("STRING", {"multiline": True}),
+                "text_i": ("STRING", {"multiline": True}),
+                "text_j": ("STRING", {"multiline": True}),
+                "text_k": ("STRING", {"multiline": True}),
+                "text_l": ("STRING", {"multiline": True}),
+                "text_m": ("STRING", {"multiline": True}),
+                "text_n": ("STRING", {"multiline": True}),
+                "text_o": ("STRING", {"multiline": True}),
+                "text_p": ("STRING", {"multiline": True}),
+                "text_q": ("STRING", {"multiline": True}),
+                "text_r": ("STRING", {"multiline": True}),
+            }
+        }
+
+    RETURN_TYPES = ("STRING",)
+    FUNCTION = "exec"
+    CATEGORY = "utils"
+    OUTPUT_NODE = True
+
+    def exec(self, action, tidy_tags, text_a=None, text_b=None, text_c=None, text_d=None, text_e=None, text_f=None, text_g=None, text_h=None,
+             text_i=None, text_j=None, text_k=None, text_l=None, text_m=None, text_n=None, text_o=None, text_p=None, text_q=None, text_r=None):
+        # Check if input is None or "undefined" and replace with an empty string
+        text_inputs = [text_a, text_b, text_c, text_d, text_e, text_f, text_g, text_h, text_i, text_j, text_k, text_l, text_m, text_n, text_o, text_p, text_q, text_r]
+        text_inputs = ["" if input_value in (None, "undefined") else input_value for input_value in text_inputs]
+
+        tidy_tags = tidy_tags == "yes"
+        out = ""
+        if action == "append":
+            out = (", " if tidy_tags else "").join(filter(None, text_inputs))
+        else:
+            if text_r is None:
+                text_r = ""
+            if text_b and text_b.startswith("/") and text_b.endswith("/"):
+                regex = text_b[1:-1]
+                out = re.sub(regex, text_r, text_a)
+            else:
+                out = text_a.replace(text_b, text_r)
+        if tidy_tags:
+            out = out.replace("  ", " ").replace(" ,", ",").replace(",,", ",").replace(",,", ",")
+        return {"ui": {"text": (out,)}, "result": (out,)}
+class StringFunction:
+    @classmethod
+    def INPUT_TYPES(s):
+        return {
+            "required": {
+                "action": (["append", "replace"], {}),
+                "tidy_tags": (["yes", "no"], {}),
+            },
+            "optional": {
+                "text_a": ("STRING", {"multiline": True}),
+                "text_b": ("STRING", {"multiline": True}),
+                "text_c": ("STRING", {"multiline": True}),
+                "text_d": ("STRING", {"multiline": True}),
+                "text_e": ("STRING", {"multiline": True}),
+                "text_f": ("STRING", {"multiline": True}),
+                "text_g": ("STRING", {"multiline": True}),
+                "text_h": ("STRING", {"multiline": True}),
+                "text_i": ("STRING", {"multiline": True}),
+                "text_j": ("STRING", {"multiline": True}),
+                "text_k": ("STRING", {"multiline": True}),
+                "text_l": ("STRING", {"multiline": True}),
+                "text_m": ("STRING", {"multiline": True}),
+                "text_n": ("STRING", {"multiline": True}),
+                "text_o": ("STRING", {"multiline": True}),
+                "text_p": ("STRING", {"multiline": True}),
+                "text_q": ("STRING", {"multiline": True}),
+                "text_r": ("STRING", {"multiline": True}),
+            }
+        }
+
+    RETURN_TYPES = ("STRING",)
+    FUNCTION = "exec"
+    CATEGORY = "utils"
+    OUTPUT_NODE = True
+
+    def exec(self, action, tidy_tags, text_a=None, text_b=None, text_c=None, text_d=None, text_e=None, text_f=None, text_g=None, text_h=None,
+             text_i=None, text_j=None, text_k=None, text_l=None, text_m=None, text_n=None, text_o=None, text_p=None, text_q=None, text_r=None):
+        # Check if input is None or "undefined" and replace with an empty string
+        text_inputs = [text_a, text_b, text_c, text_d, text_e, text_f, text_g, text_h, text_i, text_j, text_k, text_l, text_m, text_n, text_o, text_p, text_q, text_r]
+        text_inputs = ["" if input_value in (None, "undefined") else input_value for input_value in text_inputs]
+
+        tidy_tags = tidy_tags == "yes"
+        out = ""
+        if action == "append":
+            out = (", " if tidy_tags else "").join(filter(None, text_inputs))
+        else:
+            if text_r is None:
+                text_r = ""
+            if text_b and text_b.startswith("/") and text_b.endswith("/"):
+                regex = text_b[1:-1]
+                out = re.sub(regex, text_r, text_a)
+            else:
+                out = text_a.replace(text_b, text_r)
+        if tidy_tags:
+            out = out.replace("  ", " ").replace(" ,", ",").replace(",,", ",").replace(",,", ",")
+        return {"ui": {"text": (out,)}, "result": (out,)}
+
+
+NODE_CLASS_MAPPINGS = {
+    "StringFunction": StringFunction,
+}
+
+NODE_DISPLAY_NAME_MAPPINGS = {
+    "StringFunction": "String Function Tree",
+}