fixes #291

Author: wumpz

src/main/java/net/sf/jsqlparser/util/deparser/SelectDeParser.java

@@ -33,8 +33,8 @@
  */
 public class SelectDeParser implements SelectVisitor, SelectItemVisitor, FromItemVisitor, PivotVisitor {
 
-    private StringBuilder buffer;
-    private ExpressionVisitor expressionVisitor;
+    private StringBuilder buffer = new StringBuilder();
+    private ExpressionVisitor expressionVisitor = new ExpressionVisitorAdapter();
 
     public SelectDeParser() {
     }