get_issuer
Description:
Gets the TlsCertificate representing this's issuer, if known
Parameters:
| this | 
Returns:
| 
           The certificate of this's issuer, or null if this is self-signed or signed with an unknown certificate.  | 
      
Gets the TlsCertificate representing this's issuer, if known
| this | 
| 
           The certificate of this's issuer, or null if this is self-signed or signed with an unknown certificate.  |