Rebase: Don't swallow caught exception

Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: Ie485ec39ae7acc2863823fefa39494475c302079

java/com/google/gerrit/server/restapi/change/Rebase.java

@@ -165,7 +165,7 @@ public class Rebase extends RetryingRestModifyView<RevisionResource, RebaseInput
       }
     } catch (NoSuchChangeException e) {
       throw new UnprocessableEntityException(
-          String.format("Base change not found: %s", input.base));
+          String.format("Base change not found: %s", input.base), e);
     }
 
     PatchSet.Id baseId = base.patchSet().id();