fix potential NullPointerException - Bugzilla Issue 64438

WHATSNEW

@@ -1,6 +1,12 @@
 Changes from Ant 1.10.8 TO Ant 1.10.9
 =====================================
 
+Fixed bugs:
+-----------
+
+ * the ftp task could throw a NullPointerException if an error occured
+   Bugzilla Report 64438
+
 Changes from Ant 1.10.7 TO Ant 1.10.8
 =====================================
 

src/main/org/apache/tools/ant/taskdefs/optional/net/FTP.java

@@ -2611,9 +2611,10 @@ public class FTP extends Task implements FTPTaskConfig {
             }
 
         } catch (IOException ex) {
-            String cause = ex.getCause().toString();
+            final Throwable cause = ex.getCause();
             if (cause != null) {
-                if (cause.contains("java.net.SocketTimeoutException")) {
+                final String msg = cause.toString();
+                if (msg != null && msg.contains("java.net.SocketTimeoutException")) {
                     // When a read timeout occurs, inform the server that it
                     // should abort.
                     // Note that the latest commons-net (3.6) still does not