From 6125413a33464bca9fe3a57dce0c2de028904f4a Mon Sep 17 00:00:00 2001
From: Daniel Weindl <daniel.weindl@uni-bonn.de>
Date: Mon, 10 Nov 2025 19:34:25 +0100
Subject: [PATCH] Handle KeyError in CheckInitialChangeSymbols

We don't want KeyErrors in petablint output.
---
 petab/v2/lint.py | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/petab/v2/lint.py b/petab/v2/lint.py
index 178abc79..1fe83144 100644
--- a/petab/v2/lint.py
+++ b/petab/v2/lint.py
@@ -768,8 +768,15 @@ def run(self, problem: Problem) -> ValidationIssue | None:
                 if condition_id in valid_conditions:
                     continue
 
-                # we assume that all referenced condition IDs are valid
-                condition = id_to_condition[condition_id]
+                try:
+                    condition = id_to_condition[condition_id]
+                except KeyError:
+                    messages.append(
+                        f"Unable to validate changes for condition "
+                        f"{condition_id} applied at the start of "
+                        f"experiment {experiment.id}, as the condition "
+                        "does not exist."
+                    )
 
                 used_symbols = {
                     str(sym)