fix NPE in SqlppAstPrintVisitor

Change-Id: Ic5ac437366aa0eb2d60ceceeeba5b5f02d2946d2
Reviewed-on: https://asterix-gerrit.ics.uci.edu/1114
Reviewed-by: Yingyi Bu <buyingyi@gmail.com>
Sonar-Qube: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Tested-by: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Integration-Tests: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
diff --git a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppAstPrintVisitor.java b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppAstPrintVisitor.java
index 908f799..3880fa1 100644
--- a/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppAstPrintVisitor.java
+++ b/asterixdb/asterix-lang-sqlpp/src/main/java/org/apache/asterix/lang/sqlpp/visitor/SqlppAstPrintVisitor.java
@@ -132,9 +132,10 @@
     public Void visit(Projection projection, Integer step) throws AsterixException {
         if (projection.star()) {
             out.println(skip(step) + "*");
+        } else {
+            projection.getExpression().accept(this, step);
+            out.println(skip(step) + projection.getName());
         }
-        projection.getExpression().accept(this, step);
-        out.println(skip(step) + projection.getName());
         return null;
     }