tree a6c078df2c466692436149298a0cf288332aa0b0
parent 0c071662a770cbfe7f6768a791fafaa7a5e48654
author Stephen Adams <sra@google.com> 1639703809 +0000
committer Commit Bot <commit-bot@chromium.org> 1639703809 +0000

[js_ast] Prepare visitors for null-safety

`BaseVisitor<R>` has two methods that return `null`, which will not
match the generic return type with NNBD.

The fix is to make the methods abstract, and provide a convenience
specialization `BaseVisitorVoid` with the default methods.

Change-Id: I62cd69c5ed1c912b2804da5044e2cda93d70b878
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/224460
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Commit-Queue: Stephen Adams <sra@google.com>