Backport fix for OPENDJ-1252: ReadSchema example throws NPE

Matthew Swift

13.40.2013 249f365384d6e9927fc8cd3e161a789bbaf0ed47

 opendj-ldap-sdk/src/main/java/org/forgerock/opendj/ldap/schema/MatchingRule.java

@@ -371,10 +371,15 @@
        }

        if (impl == null) {
            impl = schema.getDefaultMatchingRule().impl;
            final LocalizableMessage message = WARN_MATCHING_RULE_NOT_IMPLEMENTED1
                    .get(getNameOrOID(), schema.getDefaultMatchingRule()
                            .getOID());
            final MatchingRule defaultMatchingRule = schema.getDefaultMatchingRule();
            if (defaultMatchingRule.impl == null) {
                // The default matching rule was never validated.
                defaultMatchingRule.validate(schema, warnings);
            }
            impl = defaultMatchingRule.impl;
            final LocalizableMessage message =
                    WARN_MATCHING_RULE_NOT_IMPLEMENTED1.get(getNameOrOID(), schema
                            .getDefaultMatchingRule().getOID());
            warnings.add(message);
        }