The problem

Annotating a method @Nullable communicates to tools that the method can return null. That means they can check that callers handle a returned null correctly.

Adding @Nullable may require updating callers so that they deal with the possibly-null value. This can happen for example with Kotlin callers, or with Java callers that are checked for null-safety by static-analysis tools. Alternatively, depending on the tool, it may be possible to annotate Java callers temporarily with @SuppressWarnings("nullness").

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("ReturnMissingNullable") to the enclosing element.