Make org.apache.commons.cli.help.AbstractHelpFormatter.comparator final

Author: garydgregory

src/main/java/org/apache/commons/cli/help/AbstractHelpFormatter.java

@@ -180,7 +180,7 @@ public B setOptionGroupSeparator(final String optionGroupSeparator) {
     public static final String DEFAULT_SYNTAX_PREFIX = "usage: ";
 
     /** The comparator for sorting {@link Option} collections */
-    protected Comparator<Option> comparator;
+    protected final Comparator<Option> comparator;
     /**
      * The {@link HelpAppendable} that produces the final output.
      */