code: public static void appendQuoted (@Nonnull final StringBuilder aTarget, @Nullable final String sSource)
    {
      if (sSource == null)
        aTarget.append ("null");
      else
        aTarget.append ('\'').append (sSource).append ('\'');
    }
docs: Append the provided string quoted or unquoted if it is <code>null</code>.
  
  @param aTarget
  The target to write to. May not be <code>null</code>.
  @param sSource
  Source string. May be <code>null</code>.
  @see #getQuoted(String)
  @since 9.2.0