8014814: (str) StringBuffer "null" is not appended

Reviewed-by: alanb

src/share/classes/java/lang/StringBuffer.java

@@ -335,10 +335,8 @@ import java.util.Arrays;
      * @since 1.5
      */
     @Override
-    public StringBuffer append(CharSequence s) {
-        // Note, synchronization achieved via invocations of other StringBuffer methods after
-        // narrowing of s to specific type
-        // Ditto for toStringCache clearing
+    public synchronized StringBuffer append(CharSequence s) {
+        toStringCache = null;
         super.append(s);
         return this;
     }

test/java/lang/StringBuffer/ToStringCache.java

@@ -22,7 +22,7 @@
  */
 
 /* @test
- * @bug 8013395
+ * @bug 8013395 8014814
  * @summary Test StringBuffer.toString caching
  */
 
@@ -199,6 +199,28 @@ public class ToStringCache {
         b = sb.toString();
         checkUnequal(a, b);
 
+        // Extra checks that append(null) works correctly
+
+        sb.append((String)null);
+        b = sb.toString();
+        checkUnequal(a, b);
+        a = b;
+
+        sb.append((StringBuffer)null);
+        b = sb.toString();
+        checkUnequal(a, b);
+        a = b;
+
+        sb.append((StringBuilder)null);
+        b = sb.toString();
+        checkUnequal(a, b);
+        a = b;
+
+        sb.append((CharSequence)null);
+        b = sb.toString();
+        checkUnequal(a, b);
+        a = b;
+
         // non-mutating methods
 
         // Reset to known value