Primitive and enum collections contain None despite non-nullable element annotations #777

Problem

Optional[list[T]] permits an absent collection, not None elements. JSON primitive and enum collection readers retain nullable conversion results, while generated properties expose non-nullable elements.

Reproduction

import json
from enum import Enum
from kiota_serialization_json.json_parse_node import JsonParseNode

JsonParseNode(json.loads('["a", null, 42]')).get_collection_of_primitive_values(str)
# ["a", None, None], despite Optional[list[str]]

class Colour(Enum):
    Red = "red"

JsonParseNode(json.loads('["red", null, "unknown"]')).get_collection_of_enum_values(Colour)
# [Colour.Red, None, None]

These reproductions are source-derived. CSV enum parsing filters unsuccessful results, unlike enum array parsing. Some malformed temporal/UUID values throw while other conversions return None. Model factories normally create empty models for JSON null; they are not included in this confirmed mismatch.

Source

• Public collection contracts
• Primitive mapping
• Enum mapping
• Nullable converters
• Typed model and collection assignment

Expected resolution and breaking impact

Either reflect nullable elements in abstractions, implementations and generated models, or reject null/unsuccessful conversions when promising non-nullable elements. Widening annotations is source-breaking; throwing changes behavior. Avoid casts that hide the mismatch or silent filtering of position-sensitive arrays. Cover nulls, wrong primitive shapes, temporal conversion failures and array-versus-CSV enum behavior. Coordinate runtime and generator releases.

Related cross-language audit: microsoft/kiota#8377.