Fix superclass of IfNullTypeComputer

Change-Id: I8b7e195f3127c6c5922b93070bdf29c834ea9873
Reviewed-on: https://asterix-gerrit.ics.uci.edu/1760
Sonar-Qube: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
BAD: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Reviewed-by: Yingyi Bu <buyingyi@gmail.com>
diff --git a/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/typecomputer/impl/IfNullTypeComputer.java b/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/typecomputer/impl/IfNullTypeComputer.java
index 149b35d..1384bac 100644
--- a/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/typecomputer/impl/IfNullTypeComputer.java
+++ b/asterixdb/asterix-om/src/main/java/org/apache/asterix/om/typecomputer/impl/IfNullTypeComputer.java
@@ -23,7 +23,7 @@
 import org.apache.asterix.om.types.ATypeTag;
 import org.apache.asterix.om.types.AUnionType;
 
-public class IfNullTypeComputer extends IfMissingOrNullTypeComputer {
+public class IfNullTypeComputer extends AbstractIfMissingOrNullTypeComputer {
 
     public static final IResultTypeComputer INSTANCE = new IfNullTypeComputer();