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Sarj Standards

Python · correctness

prefer-non-nullable-collection

python:prefer-non-nullable-collection

Avoid nullable list parameters when local use proves `None` and an empty list are equivalent.

Code
SARJ082
Default
error
Fix
none
Languages
python

Why

Exposing two equivalent empty states expands the function contract without preserving meaningful information.

Fix

Require the list, or accept an immutable empty default such as `Sequence[T] = ()` and materialize a list internally.

Before / after

Executed by this rule’s unit tests.

Before

Nullable list is immediately normalized

app/resolver.py · focus
def resolve(candidates: list[str] | None = None) -> list[str]:
    return candidates or []

After

Required list has one empty state

app/resolver.py · focus
def resolve(candidates: list[str]) -> list[str]:
    return candidates

Limits

  • Only module functions and constructors with a nullable list defaulted to `None` are analyzed.
  • Overrides, tests, generated code, nested captures, multiple reads, and uses that preserve `None` as a distinct state are excluded.