From dc86227d694671e24d1e70d4c20de38cae92805a Mon Sep 17 00:00:00 2001
From: Adam Dangoor <adamdangoor@gmail.com>
Date: Wed, 26 Aug 2026 14:36:19 +0100
Subject: [PATCH] Reject an empty top-level value in _string_from_json

Closes #1487

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YJDy3qA1LyNTh11zS98ukM
---
 newsfragments/1487.change.rst              |  3 +++
 src/vws_web_tools/__init__.py              | 11 +++++++++--
 tests/test_model_target_web_api_details.py | 19 ++++++++++++++++++-
 3 files changed, 30 insertions(+), 3 deletions(-)
 create mode 100644 newsfragments/1487.change.rst

diff --git a/newsfragments/1487.change.rst b/newsfragments/1487.change.rst
new file mode 100644
index 00000000..94102e57
--- /dev/null
+++ b/newsfragments/1487.change.rst
@@ -0,0 +1,3 @@
+Raise an error, rather than searching nested objects, when a Vuforia
+credentials API response has the wanted key at the top level but with
+an empty value.
diff --git a/src/vws_web_tools/__init__.py b/src/vws_web_tools/__init__.py
index 6c9e88c7..455f6929 100644
--- a/src/vws_web_tools/__init__.py
+++ b/src/vws_web_tools/__init__.py
@@ -1285,8 +1285,15 @@ def _string_from_json(
     if _is_json_object(value):
         for key in keys:
             child = value.get(key)
-            if isinstance(child, str) and child:
-                return child
+            if isinstance(child, str):
+                if child:
+                    return child
+                # An object which has the key but with an empty value is
+                # the object we were looking for, and it is malformed.
+                # Do not fall through to a nested object which happens
+                # to have the same key.
+                message = f"Response included an empty '{key}'."
+                raise ValueError(message)
         for child in value.values():
             with contextlib.suppress(ValueError):
                 return _string_from_json(value=child, keys=keys)
diff --git a/tests/test_model_target_web_api_details.py b/tests/test_model_target_web_api_details.py
index 87c68e2e..fd12a685 100644
--- a/tests/test_model_target_web_api_details.py
+++ b/tests/test_model_target_web_api_details.py
@@ -91,7 +91,7 @@ def test_string_from_json_finds_nested_values() -> None:
     """A non-empty matching string is found recursively."""
     result = vws_web_tools._string_from_json(
         value={
-            "client_id": "",
+            "unrelated": "",
             "nested": [
                 {"clientId": "client-id"},
             ],
@@ -102,6 +102,23 @@ def test_string_from_json_finds_nested_values() -> None:
     assert result == "client-id"
 
 
+def test_string_from_json_rejects_an_empty_top_level_value() -> None:
+    """An object which has the key with an empty value is not skipped."""
+    with pytest.raises(
+        expected_exception=ValueError,
+        match="Response included an empty 'client_id'",
+    ):
+        vws_web_tools._string_from_json(
+            value={
+                "client_id": "",
+                "nested": [
+                    {"clientId": "client-id"},
+                ],
+            },
+            keys=("client_id", "clientId"),
+        )
+
+
 def test_string_from_json_raises_for_missing_values() -> None:
     """A missing matching string raises a useful error."""
     with pytest.raises(