Dotty

Fix warning message for matching on redundant nulls #32973

Job	Run time
test	53m 18s
test_non_bootstrapped	0s
test_scala2_library_tasty	0s
test_windows_fast	31m 53s
community_build_a	59m 45s
MiMa	10m 33s
test_windows_full	0s
community_build_b	1h 22m 1s
community_build_c	1h 3m 9s
test_sbt	18m 7s
build-msi-package	0s
test_java8	0s
build-sdk-package / build	8m 9s
test-msi-package	0s
build-chocolatey-package / build	18s
test-chocolatey-package	0s
publish_nightly	0s
publish_release	0s
nightly_documentation	0s
open_issue_on_failure	0s
	5h 27m 13s

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