From 152bcc5def607dc8b2fe38f52d5f66fe8bcf0e47 Mon Sep 17 00:00:00 2001
From: phoneee <phoneee@gmail.com>
Date: Sun, 29 Mar 2026 16:40:25 +0700
Subject: [PATCH 1/2] fix: guard nighit, check_sara, check_marttra against
 empty input

nighit() crashed with IndexError when w2 had no consonants.
check_sara("") and check_marttra("") crashed accessing word[-1].
Add input validation with clear error messages.
---
 pythainlp/khavee/core.py             | 6 ++++++
 pythainlp/morpheme/word_formation.py | 7 ++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/pythainlp/khavee/core.py b/pythainlp/khavee/core.py
index f940e8922..dc426b322 100644
--- a/pythainlp/khavee/core.py
+++ b/pythainlp/khavee/core.py
@@ -54,6 +54,9 @@ def check_sara(self, word: str) -> str:
         sara = []
         countoa = 0
 
+        if not word:
+            return ""
+
         # In case of การันย์
         if "์" in word[-1]:
             word = word[:-2]
@@ -253,6 +256,9 @@ def check_marttra(self, word: str) -> str:
         word = self.handle_karun_sound_silence(word)
         word = remove_tonemark(word)
 
+        if not word:
+            return ""
+
         # Check for ำ at the end (represents "am" sound, ends with m)
         if word[-1] == "ำ":
             return "กม"
diff --git a/pythainlp/morpheme/word_formation.py b/pythainlp/morpheme/word_formation.py
index 63453a25e..567a3e2c0 100644
--- a/pythainlp/morpheme/word_formation.py
+++ b/pythainlp/morpheme/word_formation.py
@@ -38,7 +38,12 @@ def nighit(w1: str, w2: str) -> str:
     newword = []
     newword.append(list_w1[0])
     newword.append("ั")
-    consonant_start = [i for i in list_w2 if i in set(thai_consonants)][0]
+    consonants_in_w2 = [i for i in list_w2 if i in set(thai_consonants)]
+    if not consonants_in_w2:
+        raise ValueError(
+            f"w2 '{w2}' contains no Thai consonants."
+        )
+    consonant_start = consonants_in_w2[0]
     if consonant_start in ["ก", "ช", "ค", "ข", "ง"]:
         newword.append("ง")
     elif consonant_start in ["จ", "ฉ", "ช", "ฌ"]:

From e8ba54a3e0363d29023d2f1f7a79c37b89ac2085 Mon Sep 17 00:00:00 2001
From: Arthit Suriyawongkul <arthit@gmail.com>
Date: Sun, 29 Mar 2026 22:08:23 +0100
Subject: [PATCH 2/2] Update pythainlp/morpheme/word_formation.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
---
 pythainlp/morpheme/word_formation.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pythainlp/morpheme/word_formation.py b/pythainlp/morpheme/word_formation.py
index 567a3e2c0..45b161fe2 100644
--- a/pythainlp/morpheme/word_formation.py
+++ b/pythainlp/morpheme/word_formation.py
@@ -41,7 +41,7 @@ def nighit(w1: str, w2: str) -> str:
     consonants_in_w2 = [i for i in list_w2 if i in set(thai_consonants)]
     if not consonants_in_w2:
         raise ValueError(
-            f"w2 '{w2}' contains no Thai consonants."
+            f"w2 {w2!r} contains no Thai consonants."
         )
     consonant_start = consonants_in_w2[0]
     if consonant_start in ["ก", "ช", "ค", "ข", "ง"]: