code: public void setPrivateKeyValid(Date privateKeyValid) {
          if (privateKeyValid == null) {
              this.privateKeyValid = null;
          } else {
              this.privateKeyValid = (Date)privateKeyValid.clone();
          }
      }
docs: Sets the privateKeyValid criterion. The specified date must fall
  within the private key validity period for the
  {@code X509Certificate}. If {@code null}, no privateKeyValid
  check will be done.
  <p>
  Note that the {@code Date} supplied here is cloned to protect
  against subsequent modifications.
  
  @param privateKeyValid the {@code Date} to check (or
  {@code null})
  @see #getPrivateKeyValid