Rename parameter to match override

Author: garydgregory

src/main/java/org/apache/commons/io/output/NullWriter.java

@@ -122,10 +122,10 @@ public void write(final char[] chr, final int st, final int end) {
 
     /**
      * Does nothing - output to {@code /dev/null}.
-     * @param idx The character to write
+     * @param b The character to write.
      */
     @Override
-    public void write(final int idx) {
+    public void write(final int b) {
         //to /dev/null
     }