qos: QOS fails with 'Attribute is not defined: QOS_POLICY'

Motivation: Find out where in the code we throw the above error and resolve it.

Modification: Removal of redundant qos policy logic.

Result: Instead of checking if the qos_policy attribute is defined AND null, we will check if it is present using one of the predefined methods.
If not, set it to null and resume previous logic.

Acked-by: Tigran Mkrtchyan
Target: master, 10.2, 10.1, 10.0, 9.2
Require-book: no
Require-notes: yes

modules/dcache-qos/src/main/java/org/dcache/qos/services/engine/provider/PolicyBasedQoSProvider.java

@@ -59,10 +59,7 @@ LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  */
 package org.dcache.qos.services.engine.provider;
 
-import static org.dcache.qos.util.QoSPermissionUtils.canModifyQos;
-
 import diskCacheV111.util.CacheException;
-import diskCacheV111.util.PermissionDeniedCacheException;
 import diskCacheV111.util.PnfsId;
 import java.util.Collections;
 import java.util.EnumSet;
@@ -71,6 +68,7 @@ LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 import java.util.Optional;
 import java.util.Set;
 import javax.security.auth.Subject;
+
 import org.dcache.namespace.FileAttribute;
 import org.dcache.poolmanager.SerializablePoolMonitor;
 import org.dcache.qos.QoSDiskSpecification;
@@ -115,27 +113,18 @@ public FileQoSRequirements fetchRequirements(FileQoSUpdate update) throws QoSExc
             return null;
         }
 
-        FileAttributes attributes = descriptor.getAttributes();
-        if (attributes.isDefined(FileAttribute.QOS_POLICY) && attributes.getQosPolicy() == null) {
-            /*
-             * This is a lazily discovered change, so
-             * as a matter of consistency it calls for removal
-             * of the pnfsid from the engine's tracking tables.
-             */
-            engineDao.delete(update.getPnfsId());
-            return super.fetchRequirements(update, descriptor);
-        }
-
         return fetchRequirements(update, descriptor);
     }
 
     @Override
     public FileQoSRequirements fetchRequirements(FileQoSUpdate update, FileQoSRequirements descriptor)
           throws QoSException {
         FileAttributes attributes = descriptor.getAttributes();
-        String name = attributes.getQosPolicy();
+
+        String name = attributes.getQosPolicyIfPresent().orElse(null);
 
         if (name == null) {
+            engineDao.delete(update.getPnfsId());
             return super.fetchRequirements(update, descriptor);
         }