Return an empty collection instead of null
io.moderne.nullability.ReturnEmptyCollectionInsteadOfNullio.moderne.recipe:rewrite-nullabilityRewrites a bare return null; to return an empty immutable collection when the enclosing method's declared return type is java.util.List, java.util.Set, java.util.Collection, or java.util.Map (raw or generic): List and Collection become Collections.emptyList(), Set becomes Collections.emptySet(), and Map becomes Collections.emptyMap() (each statically imported). Returning an empty collection rather than null spares every caller a null check, but a caller that distinguishes null from empty observes a different result, so this is a behavior change and every rewritten return is flagged for review. Only the literal return null; statement is rewritten — a return someNullableExpr; is left untouched — and a method whose return is annotated @Nullable is skipped, since there the null is intended. The recipe is gated on @NullMarked scope, idempotent, and conservative; only Java sources are modified.
Usage
This recipe has no required configuration options. You’ll need the Moderne CLI configured before running the command below.
mod run . --recipe io.moderne.nullability.ReturnEmptyCollectionInsteadOfNullIf the recipe isn’t available locally, install it with:
mod config recipes jar install io.moderne.recipe:rewrite-nullability:0.3.1Options
| Name | Type | Description |
|---|---|---|
annotatedPackages | String | Comma-separated package prefixes to limit the fix to (matching NullAway's AnnotatedPackages option). When unset, the recipe fixes all packages.e.g. com.example |
Data tables
Structured output this recipe can produce.
- Null-safety fixes by rungEach residual null-safety fix applied, tagged with the precedence rung that produced it, so the share bottoming out at a last-resort `requireNonNull` assertion can be tracked.
io.moderne.nullability.table.NullFixes - Declined null-safety fixes needing reviewEach site the recipe declined to auto-fix because the fix is a design decision (the value is explicitly `null` on some path, so the slot likely should be `@Nullable`), for human triage.
io.moderne.nullability.table.DeclinedNullFixes - Source files that had resultsSource files that were modified by the recipe run.
org.openrewrite.table.SourcesFileResults - Source files that had search resultsSearch results that were found during the recipe run.
org.openrewrite.table.SearchResults - Source files that errored on a recipeThe details of all errors produced by a recipe run.
org.openrewrite.table.SourcesFileErrors - Recipe performanceStatistics used in analyzing the performance of recipes.
org.openrewrite.table.RecipeRunStats