Line 316 in fastapi/_compat/v2.py was untested, causing coverage to fail at 99%. The line is a continue statement that skips NoneType when iterating union args in serialize_sequence_value.

Root Cause

Existing tests used list[str] | None, which orders union args as (list[str], NoneType). The loop processes list[str] first and breaks, never reaching the continue statement for NoneType.

Changes

• Updated test_serialize_sequence_value_with_none_first_in_union to use explicit Union[None, list[str]] syntax
• This places NoneType first in union args, exercising the continue statement before processing the list type

# Before: list[str] | None → union args are (list[str], NoneType)
field_info = FieldInfo(annotation=list[str] | None)

# After: Union[None, list[str]] → union args are (NoneType, list[str])  
field_info = FieldInfo(annotation=Union[None, list[str]])

Coverage now reaches 100%.

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.