JAL-3048 fix NPE in file chooser callbacks map

diff --git a/src/jalview/io/JalviewFileChooser.java b/src/jalview/io/JalviewFileChooser.java
index 7909d0c..88a337a 100755 (executable)
--- a/src/jalview/io/JalviewFileChooser.java
+++ b/src/jalview/io/JalviewFileChooser.java
@@ -37,6 +37,7 @@ import java.beans.PropertyChangeEvent;
 import java.beans.PropertyChangeListener;
 import java.io.File;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.StringTokenizer;
@@ -64,7 +65,7 @@ public class JalviewFileChooser extends JFileChooser implements DialogRunnerI,
 {
   private static final long serialVersionUID = 1L;
 
-  private Map<Object, Runnable> callbacks;
+  private Map<Object, Runnable> callbacks = new HashMap<>();
   
   File selectedFile = null;