DiganosticCollector.report(null) should throw NPE
<testcase>
import javax.tools.*;
public class Foo {
    public static void main(String... arg) throws Throwable {
        DiagnosticCollector<JavaFileObject> dl
                = new DiagnosticCollector<JavaFileObject>();
        dl.report(null);
        throw new Exception("Expected null pointer exception not thrown");
    }
}
</testcase>

<output>
bash-3.00$ java Foo
Exception in thread "main" java.lang.Exception: Expected null pointer exception not thrown
        at Foo.main(Foo.java:7)
</output>

<java-version>
bash-3.00$ java -version
java version "1.6.0-rc"
Java(TM) SE Runtime Environment (build 1.6.0-rc-b92)
</java-version>