Fixing performance regression

diff --git a/src/main/java/org/apache/xml/security/utils/UnsyncByteArrayOutputStream.java b/src/main/java/org/apache/xml/security/utils/UnsyncByteArrayOutputStream.java
index 729188e..a4af869 100644
--- a/src/main/java/org/apache/xml/security/utils/UnsyncByteArrayOutputStream.java
+++ b/src/main/java/org/apache/xml/security/utils/UnsyncByteArrayOutputStream.java
@@ -93,7 +93,6 @@
     @Override
     public void close() throws IOException {
         bufCache.remove();
-        buf = null;
     }
 
     private void expandSize(int newPos) {