Creating a JMXServiceURL with null protocol information, defaults to using jmxmp.

This is odd, as jmxmp was never part of the JDK, although it did exist as a separate component.

If an application creates a JMXServiceURL with missing information, e.g. creating a JMXConnectorServer with a null URL, the error is:

java.net.MalformedURLException: Unsupported protocol: jmxmp
        at java.management/javax.management.remote.JMXConnectorServerFactory.newJMXConnectorServer(JMXConnectorServerFactory.java:319)

This is misleading, and not useful. A JDK would not be expected to have jmxmp available, and there is no information about the protocol.

A null protocol would be more useful simply being illegal, perhaps a MalformedURLException.
 
Will require api doc updates.