Refine StringSequence checkstyle suppression

See gh-23440

Author: philwebb

src/checkstyle/checkstyle-suppressions.xml

@@ -42,5 +42,5 @@
 	<suppress files="SampleJUnitVintageApplicationTests" checks="SpringJUnit5" />
 	<suppress files="[\\/]spring-boot-docs[\\/]" checks="SpringJavadoc" message="\@since" />
 	<suppress files="[\\/]spring-boot-smoke-tests[\\/]" checks="SpringJavadoc" message="\@since" />
-	<suppress files="StringSequence" checks="SpringMethodVisibility"/>
+	<suppress files="StringSequence" checks="SpringMethodVisibility" message="isEmpty"/>
 </suppressions>