checkstyle: declare org.jetbrains and javax.annotation Nullable's and NotNull/Nonnull as illegal imports

Author: evermind-zz

checkstyle/checkstyle.xml

@@ -95,7 +95,9 @@
         <!-- Checks for imports                              -->
         <!-- See https://checkstyle.org/config_import.html -->
         <module name="AvoidStarImport"/>
-        <module name="IllegalImport"/> <!-- defaults to sun.* packages -->
+        <module name="IllegalImport"> <!-- defaults to sun.* packages -->
+            <property name="illegalClasses" value="org.jetbrains.annotations.Nullable, org.jetbrains.annotations.NotNull, javax.annotation.Nullable, javax.annotation.Nonnull" />
+        </module>
         <module name="RedundantImport"/>
         <module name="UnusedImports"/>