From 8da1a4ef4086a1c2ac3ab4dd4e1d5a23d2baac95 Mon Sep 17 00:00:00 2001
From: Guillaume Nodet <gnodet@gmail.com>
Date: Wed, 9 Sep 2026 06:08:36 +0000
Subject: [PATCH] CAMEL-24651: Fix NPE in ExceptionHelper.stackTraceToString()
 when exception is null

When ${exception.stacktrace} is evaluated on an exchange that has no
exception, LanguageHelper.exceptionStacktrace() calls
ExceptionHelper.stackTraceToString(null), which then NPEs on
e.printStackTrace(printWriter).

Add a null guard in ExceptionHelper.stackTraceToString() so that it
returns null when the supplied Throwable is null, consistent with the
existing behaviour of LanguageHelper.exceptionMessage().
---
 .../java/org/apache/camel/language/simple/SimpleTest.java | 8 ++++++++
 .../java/org/apache/camel/support/ExceptionHelper.java    | 5 ++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/core/camel-core/src/test/java/org/apache/camel/language/simple/SimpleTest.java b/core/camel-core/src/test/java/org/apache/camel/language/simple/SimpleTest.java
index 2bb10c6cc3ac2..9e14b4bf6da3e 100644
--- a/core/camel-core/src/test/java/org/apache/camel/language/simple/SimpleTest.java
+++ b/core/camel-core/src/test/java/org/apache/camel/language/simple/SimpleTest.java
@@ -641,6 +641,14 @@ public void testExceptionStacktrace() {
         assertTrue(out.contains("at org.apache.camel.language."));
     }
 
+    @Test
+    public void testExceptionStacktraceNoException() {
+        // CAMEL-24651
+        String out = context.resolveLanguage("simple").createExpression("${exception.stacktrace}").evaluate(exchange,
+                String.class);
+        assertNull(out);
+    }
+
     @Test
     public void testException() {
         exchange.setException(new IllegalArgumentException("Just testing"));
diff --git a/core/camel-support/src/main/java/org/apache/camel/support/ExceptionHelper.java b/core/camel-support/src/main/java/org/apache/camel/support/ExceptionHelper.java
index d1e6849546b90..1f37fc3a2b9dd 100644
--- a/core/camel-support/src/main/java/org/apache/camel/support/ExceptionHelper.java
+++ b/core/camel-support/src/main/java/org/apache/camel/support/ExceptionHelper.java
@@ -33,9 +33,12 @@ private ExceptionHelper() {
      * Dumps the stack trace from the given exception to a String
      *
      * @param  e the exception to print the stack trace
-     * @return   A string instance with the stack trace for the given exception
+     * @return   A string instance with the stack trace for the given exception, or null if the exception is null
      */
     public static String stackTraceToString(Throwable e) {
+        if (e == null) {
+            return null;
+        }
         final StringWriter writer = new StringWriter();
         final PrintWriter printWriter = new PrintWriter(writer, true);
         e.printStackTrace(printWriter);