Index: src/test/org/apache/lucene/index/TestIndexReader.java
===================================================================
--- src/test/org/apache/lucene/index/TestIndexReader.java	(revision 515527)
+++ src/test/org/apache/lucene/index/TestIndexReader.java	(working copy)
@@ -981,7 +981,7 @@
       try {
         IndexReader reader = IndexReader.open(dir);
         fail("expected CorruptIndexException");
-      } catch (FileNotFoundException e) {
+      } catch (IOException e) {
         // expected
       }
 
@@ -991,7 +991,7 @@
       try {
         IndexReader reader = IndexReader.open(dir);
         fail("expected CorruptIndexException");
-      } catch (FileNotFoundException e) {
+      } catch (IOException e) {
         // expected
       }
     }
Index: src/java/org/apache/lucene/index/SegmentInfos.java
===================================================================
--- src/java/org/apache/lucene/index/SegmentInfos.java	(revision 515527)
+++ src/java/org/apache/lucene/index/SegmentInfos.java	(working copy)
@@ -113,7 +113,7 @@
   public static long getCurrentSegmentGeneration(Directory directory) throws IOException {
     String[] files = directory.list();
     if (files == null)
-      throw new IOException("Cannot read directory " + directory);
+      throw new IOException("cannot read directory " + directory + ": list() returned null");
     return getCurrentSegmentGeneration(files);
   }
 
@@ -477,14 +477,14 @@
         if (0 == method) {
           if (directory != null) {
             files = directory.list();
+            if (files == null)
+              throw new IOException("cannot read directory " + directory + ": list() returned null");
           } else {
             files = fileDirectory.list();
+            if (files == null)
+              throw new IOException("cannot read directory " + fileDirectory + ": list() returned null");
           }
 
-          if (files == null) {
-            throw new FileNotFoundException("no segments* file found in directory " + directory + ": list() returned null");
-          }
-
           gen = getCurrentSegmentGeneration(files);
 
           if (gen == -1) {
Index: src/java/org/apache/lucene/index/IndexFileDeleter.java
===================================================================
--- src/java/org/apache/lucene/index/IndexFileDeleter.java	(revision 515527)
+++ src/java/org/apache/lucene/index/IndexFileDeleter.java	(working copy)
@@ -84,6 +84,8 @@
     IndexFileNameFilter filter = IndexFileNameFilter.getFilter();
 
     String[] files = directory.list();
+    if (files == null)
+      throw new IOException("cannot read directory " + directory + ": list() returned null");
 
     for (int i = 0; i < files.length; i++) {
 
Index: src/java/org/apache/lucene/index/SegmentInfo.java
===================================================================
--- src/java/org/apache/lucene/index/SegmentInfo.java	(revision 515527)
+++ src/java/org/apache/lucene/index/SegmentInfo.java	(working copy)
@@ -236,6 +236,9 @@
         // code.  So we must fallback to the original
         // directory list check:
         String[] result = dir.list();
+        if (result == null)
+          throw new IOException("cannot read directory " + dir + ": list() returned null");
+        
         String pattern;
         pattern = name + ".s";
         int patternLength = pattern.length();
Index: src/java/org/apache/lucene/store/Directory.java
===================================================================
--- src/java/org/apache/lucene/store/Directory.java	(revision 515527)
+++ src/java/org/apache/lucene/store/Directory.java	(working copy)
@@ -42,7 +42,11 @@
    * this Directory instance). */
   protected LockFactory lockFactory;
 
-  /** Returns an array of strings, one for each file in the directory. */
+  /** Returns an array of strings, one for each file in the
+   * directory.  This method may return null (for example for
+   * {@link FSDirectory} if the underlying directory doesn't
+   * exist in the filesystem or there are permissions
+   * problems).*/
   public abstract String[] list()
        throws IOException;
 
@@ -154,6 +158,10 @@
    */
   public static void copy(Directory src, Directory dest, boolean closeDirSrc) throws IOException {
       final String[] files = src.list();
+
+      if (files == null)
+        throw new IOException("cannot read directory " + src + ": list() returned null");
+
       byte[] buf = new byte[BufferedIndexOutput.BUFFER_SIZE];
       for (int i = 0; i < files.length; i++) {
         IndexOutput os = null;
Index: src/java/org/apache/lucene/store/FSDirectory.java
===================================================================
--- src/java/org/apache/lucene/store/FSDirectory.java	(revision 515527)
+++ src/java/org/apache/lucene/store/FSDirectory.java	(working copy)
@@ -239,7 +239,7 @@
     if (directory.exists()) {
       String[] files = directory.list(IndexFileNameFilter.getFilter());            // clear old files
       if (files == null)
-        throw new IOException("Cannot read directory " + directory.getAbsolutePath());
+        throw new IOException("cannot read directory " + directory.getAbsolutePath() + ": list() returned null");
       for (int i = 0; i < files.length; i++) {
         File file = new File(directory, files[i]);
         if (!file.delete())