From 822ee0479afcc500c72f16b7fa972dc99c8bf5d5 Mon Sep 17 00:00:00 2001
From: kiramt <k.mourao@dundee.ac.uk>
Date: Wed, 8 Nov 2017 07:59:44 +0000
Subject: [PATCH] JAL-2674 Added missing null check

---
 src/jalview/datamodel/HiddenColumns.java |   15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/jalview/datamodel/HiddenColumns.java b/src/jalview/datamodel/HiddenColumns.java
index 399e083..da91f7b 100644
--- a/src/jalview/datamodel/HiddenColumns.java
+++ b/src/jalview/datamodel/HiddenColumns.java
@@ -907,16 +907,19 @@ public class HiddenColumns
     try
     {
       LOCK.writeLock().lock();
-      Iterator<int[]> it = hiddenColumns.iterator();
-      while (it.hasNext())
+      if (hiddenColumns != null)
       {
-        int[] region = it.next();
-        for (int j = region[0]; j < region[1] + 1; j++)
+        Iterator<int[]> it = hiddenColumns.iterator();
+        while (it.hasNext())
         {
-          sel.addElement(j);
+          int[] region = it.next();
+          for (int j = region[0]; j < region[1] + 1; j++)
+          {
+            sel.addElement(j);
+          }
         }
+        hiddenColumns = null;
       }
-      hiddenColumns = null;
     } finally
     {
       LOCK.writeLock().unlock();
-- 
1.7.10.2