Consider the following code:

----------------------------------------------------------
import javax.print.PrintServiceLookup;
import java.util.Arrays;

public class PS {

    public static void main(String[] args) {
        final boolean registered = PrintServiceLookup.registerService(null);
        System.out.println("registered? " + registered);
        System.out.println("services = " + Arrays.toString(PrintServiceLookup.lookupPrintServices(null, null)));
    }
}
----------------------------------------------------------

After running it v.s. JDK8 updates the output will contain

----
registered? true
...
----

and the list of services with null among them.

This doesn't look like conforming to the spec of the methods:

http://docs.oracle.com/javase/8/docs/api/javax/print/PrintServiceLookup.html#registerService-javax.print.PrintService-
http://docs.oracle.com/javase/8/docs/api/javax/print/PrintServiceLookup.html#lookupPrintServices-javax.print.DocFlavor-javax.print.attribute.AttributeSet-

The spec needs to be clarified or behavior corrected.