handle null shoulder

Author: qqmyers

src/main/java/edu/harvard/iq/dataverse/pidproviders/AbstractPidProvider.java

@@ -347,7 +347,9 @@ public GlobalId parsePersistentId(String protocol, String authority, String iden
 
         if(isCaseInsensitive) {
             identifier = identifier.toUpperCase();
-            comparableShoulder = comparableShoulder.toUpperCase();
+            if(comparableShoulder != null) {
+                comparableShoulder = comparableShoulder.toUpperCase();
+            }
         }
         // Check authority/identifier if this is a provider that manages specific
         // identifiers