docs: public void setBoundary (@Nonnull final byte [] aBoundary) throws MultipartIllegalBoundaryException
    {
      ValueEnforcer.notNull (aBoundary, "Boundary");
      if (aBoundary.length != m_nBoundaryLength - BOUNDARY_PREFIX.length)
        throw new MultipartIllegalBoundaryException ("The length of a boundary token can not be changed");
      System.arraycopy (aBoundary, 0, m_aBoundary, BOUNDARY_PREFIX.length, aBoundary.length);
    }