fix: None crash in providers, _merge_deepest loop, lock-file false positives, stage() race, cache TTL, config merge, changelog indent, template check

devgen/providers/openai.py

@@ -17,4 +17,4 @@ class OpenaiProvider(BaseProvider):
             messages=[{"role": "user", "content": prompt}],
             **kwargs,
         )
-        return response.choices[0].message.content
+        return response.choices[0].message.content or ""