mdtmFile can return null

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/net/trunk@1782001 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/main/java/examples/ftp/FTPClientExample.java b/src/main/java/examples/ftp/FTPClientExample.java
index 79af91e..c633558 100644
--- a/src/main/java/examples/ftp/FTPClientExample.java
+++ b/src/main/java/examples/ftp/FTPClientExample.java
@@ -410,8 +410,12 @@
                 }
                 if (mdtm) {
                     FTPFile f = ftp.mdtmFile(remote);
-                    System.out.println(f.getRawListing());
-                    System.out.println(f.toFormattedString(displayTimeZoneId));
+                    if (f != null) {
+                        System.out.println(f.getRawListing());
+                        System.out.println(f.toFormattedString(displayTimeZoneId));
+                    } else {
+                        System.out.println("File not found");                        
+                    }
                 }
                 if (mlst) {
                     FTPFile f = ftp.mlistFile(remote);