RFR [13] 8224973: URLStreamHandler.openConnection(URL,Proxy) - spec and implementation mismatch

[Chris Hegarty]

The current default implementation of openConnection(URL,Proxy) simply
throws UnsupportedOperationException. Pedantically, this violates its
own specification, since it does not throw IllegalArgumentException when
passed a null value.

To resolve this, the default implementation should be updated and
specified. Trivially, perform null argument checking, and subsequently
throw UnsupportedOperationException ( since the URL stream handler
implementation can realistically do nothing more ).

Webrev:
  https://cr.openjdk.java.net/~chegar/8224973/webrev.00/

CSR:
  https://bugs.openjdk.java.net/browse/JDK-8225047

-Chris.

P.S. There are a number of these minor API / default implementation
issues in the java.net package, resulting from evolution over the years.