code: public static String getString(String key, @CheckForNull String def) {
          return getString(key, def, Level.CONFIG);
      }
docs: Gets the system property indicated by the specified key, or a default value.
  This behaves just like {@link System#getProperty(java.lang.String, java.lang.String)}, except
  that it also consults the {@link ServletContext}'s "init" parameters.
  
  @param      key   the name of the system property.
  @param      def   a default value.
  @return     the string value of the system property,
  or {@code null} if the property is missing and the default value is {@code null}.
  
  @exception  NullPointerException if {@code key} is {@code null}.
  @exception  IllegalArgumentException if {@code key} is empty.