fix(jsonschema): guard against empty items list in create_array_type#1352
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Union[tuple([])] raises TypeError when items=[] in an array schema. Add an early-return to list[Any] for the empty case, matching the existing guard pattern in schema_to_type(). Also handle single-type lists without wrapping in Union. Fixes PrefectHQ#1351
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What's broken
jsonschema_to_typecrashes withTypeError: Cannot take a Union of no types.when an array schema hasitemsset to an empty list ([]), which is valid JSON Schema for a zero-element positional tuple. Any caller that generates such a schema — for example, an LLM emitting a function signature with no positional items — will hit this unconditionally.Why it happens
In
create_array_type(), whenitemsis a list, the code collectsitem_typesby iterating over it and then callsUnion[tuple(item_types)]. When the list is empty,Union[()]raisesTypeError: Cannot take a Union of no types.The analogous code inschema_to_type()already usesUnion[tuple(types)] if len(types) > 1 else types[0]to guard this, butcreate_array_typehad no such guard.Fix
Added an early path in the
isinstance(items, list)branch: ifitem_typesis empty, fall back tolist[Any]. For the single-type case, skip theUnionwrapper entirely (matching theschema_to_typepattern). This keeps the change minimal — 6 lines touched.Test
Added
test_empty_items_list_does_not_crashtoTestArrayTypes: passes{"type": "array", "items": []}tojsonschema_to_typeand asserts the returned type validates a mixed list without raising.Fixes #1351