RFR (JAXP): 8144966: Catalog API: Null handling and reference to Reader

[huizhe wang]

Hi,

This is an improvement to the new Catalog API on null handling. At the 
package level, a null argument shall result in NPE. However, an 
exception was made to the methods in CatalogManager so that they can 
used conveniently. With this request, we're in favor of consistency over 
the minor convenience, which means a resolver can no longer be created by:
          CatalogManager.catalogResolver(null);

Instead, the following may be used to achieve the same result:
         CatalogManager.catalogResolver(CatalogFeatures.defaults());

While path can be empty, it can no longer be null. The following then 
would also get a NPE:
         CatalogManager.catalogResolver(CatalogFeatures.defaults(), null);

In consistence with ignoring invalid catalogs as required by the Catalog 
standard, the statements that required CatalogException when no catalog 
is found are removed.

JBS: https://bugs.openjdk.java.net/browse/JDK-8144966
webrev: http://cr.openjdk.java.net/~joehw/jdk9/8144966/webrev/

Please review.

Thanks,
Joe