code: public void setTargetCertConstraints(CertSelector selector) {
          if (selector != null)
              certSelector = (CertSelector) selector.clone();
          else
              certSelector = null;
      }
docs: Sets the required constraints on the target certificate.
  The constraints are specified as an instance of
  {@code CertSelector}. If {@code null}, no constraints are
  defined.
  
  <p>Note that the {@code CertSelector} specified is cloned
  to protect against subsequent modifications.
  
  @param selector a {@code CertSelector} specifying the constraints
  on the target certificate (or {@code null})
  @see #getTargetCertConstraints