code: @CheckForNull
      public static Boolean optBoolean(String name) {
          String v = getString(name);
          return v == null ? null : Boolean.parseBoolean(v);
      }
docs: Returns {@link Boolean#TRUE} if the named system property exists and is equal to the string {@code "true}
  (ignoring case), returns {@link Boolean#FALSE} if the system property exists and doesn't equal {@code "true}
  otherwise returns {@code null} if the named system property does not exist.
  
  @param name the system property name.
  @return {@link Boolean#TRUE}, {@link Boolean#FALSE} or {@code null}
  @since 2.16