fix(types): parse null and {} as empty dspy.ToolCalls

Models in JSON mode (e.g. DeepSeek-V4-Flash with JSONAdapter) often write
"tool_calls": null or {} to mean "no tool calls". ToolCalls accepted [] but
rejected both, so ReActV2 ended its loop with parse_error and the forced
submit raised AdapterParseError.

Treat None and {} like [] in ToolCalls.validate_input. Optional fields
(ToolCalls | None) still validate None as None.

Amp-Thread-ID: https://ampcode.com/threads/T-01a126ab-8118-77c7-a811-67f49e5f20cd
Co-authored-by: Isaac Miller <isaac@cmpnd.ai>

Author: ampagent

dspy/adapters/types/tool.py

@@ -412,6 +412,10 @@ def validate_input(cls, data: Any):
         if isinstance(data, cls):
             return data
 
+        # Models in JSON mode often write `null` or `{}` to mean "no tool calls"; treat them like `[]`.
+        if data is None or data == {}:
+            return {"tool_calls": []}
+
         # Handle case where data is a list of dicts with either DSPy or provider-shaped tool call keys.
         if isinstance(data, list) and all(isinstance(item, dict) and _is_tool_call_dict(item) for item in data):
             return {"tool_calls": [cls.ToolCall(**_normalize_tool_call_dict(item)) for item in data]}

tests/adapters/test_tool.py

@@ -656,6 +656,10 @@ def test_toolcalls_vague_match():
     assert len(tc.tool_calls) == 1
     assert tc.tool_calls[0].args == {"query": "hello"}
 
+    # `null` and `{}` mean "no tool calls", like `[]`.
+    for empty in (None, {}, []):
+        assert ToolCalls.model_validate(empty).tool_calls == []
+
     # Invalid input should raise ValueError
     with pytest.raises(ValueError):
         ToolCalls.model_validate({"foo": "bar"})

tests/predict/test_react_v2.py

@@ -1,4 +1,5 @@
 import asyncio
+import json
 
 import pytest
 
@@ -199,6 +200,19 @@ def test_react_v2_forced_submit_on_empty_tool_calls():
     assert lm.history[1]["kwargs"].get("reasoning_effort") is None
 
 
+@pytest.mark.parametrize("empty_tool_calls", [None, {}])
+def test_react_v2_json_null_or_empty_tool_calls_mean_no_tool_calls(empty_tool_calls):
+    adapter = dspy.JSONAdapter()
+    lm = dspy.utils.DummyLM([{"next_thought": "Nothing to call.", "tool_calls": empty_tool_calls}] * 2, adapter=adapter)
+
+    with dspy.context(lm=lm, adapter=adapter):
+        with pytest.raises(ValueError, match="after empty_tool_calls: no submit call"):
+            dspy.ReActV2("question -> answer", tools=[])(question="cats")
+
+    assert f'"tool_calls": {json.dumps(empty_tool_calls)}' in lm.history[0]["outputs"][0]
+    assert len(lm.history) == 2
+
+
 def test_react_v2_forced_submit_with_native_flag_but_unsupported_lm():
     adapter = dspy.JSONAdapter(use_native_function_calling=True)
     lm = dspy.utils.DummyLM(