Fix signer behaviour for broken CRLs

internal/x509/revoking/revoking.go

@@ -191,10 +191,12 @@ func (r *X509Revoking) GetCRL(number *big.Int) (*CRLInformation, error) {
 			r.logger.WithError(err).Warn("could not parse CRL")
 		}
 
-		stillValid := list.ThisUpdate.Add(maximumCRLLifetime).After(time.Now().UTC())
+		if list != nil {
+			stillValid := list.ThisUpdate.Add(maximumCRLLifetime).After(time.Now().UTC())
 
-		if number != nil || stillValid {
+			if number != nil || stillValid {
-			return &CRLInformation{CRL: crl, Number: list.Number, NextUpdate: list.NextUpdate}, nil
+				return &CRLInformation{CRL: crl, Number: list.Number, NextUpdate: list.NextUpdate}, nil
+			}
 		}
 	}