update

Author: bit4woo

.gitignore

@@ -5,3 +5,4 @@
 *.iml
 .DS_Store
 .classpath
+.project

src/burp/BurpExtender.java

@@ -366,7 +366,11 @@ public void processHttpMessage(int toolFlag, boolean messageIsRequest, IHttpRequ
 								isRequestChanged = true;
 
 							} else if (entry.getType().equals(ConfigEntry.Action_Append_To_header_value) && entry.isEnable()) {
-								value = headers.get(key) + value;
+								String oldValue = headers.get(key);
+								if (oldValue == null) {
+									oldValue = "";
+								}
+								value = oldValue + value;
 								headers.put(key, value);
 								isRequestChanged = true;
 								//stdout.println("2222"+value);