Remove usage of JetBrains' NotNull annotation and forbid future usage

Author: marcphilipp

junit-jupiter-engine/src/test/java/org/junit/jupiter/api/extension/CloseableResourceIntegrationTests.java

@@ -14,7 +14,6 @@
 
 import java.util.Map;
 
-import org.jetbrains.annotations.NotNull;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.engine.AbstractJupiterTestEngineTests;
 
@@ -39,7 +38,6 @@ void closesCloseableResourcesInExtensionContext(ExtensionContext extensionContex
 store.put("baz", reportEntryOnClose(extensionContext, "3"));
 }
 
-@NotNull
 private ExtensionContext.Store.CloseableResource reportEntryOnClose(ExtensionContext extensionContext,
 String key) {
 return () -> extensionContext.publishReportEntry(Map.of(key, "closed"));

src/checkstyle/checkstyleMain.xml

@@ -17,6 +17,9 @@
 <property name="processJavadoc" value="true" />
 </module>
 <module name="AvoidStarImport"/>
+<module name="IllegalImport">
+<property name="illegalPkgs" value="org.jetbrains.annotations" />
+</module>
 </module>
 
 <module name="JavadocPackage" />

src/checkstyle/checkstyleTest.xml

@@ -9,6 +9,9 @@
 <property name="processJavadoc" value="true" />
 </module>
 <module name="AvoidStarImport"/>
+<module name="IllegalImport">
+<property name="illegalPkgs" value="org.jetbrains.annotations" />
+</module>
 </module>
 
 <module name="SuppressWarningsFilter" />