code: public Observable<Page<CertificateIssuerItem>> getCertificateIssuersNextAsync(final String nextPageLink) {
          return getCertificateIssuersNextWithServiceResponseAsync(nextPageLink)
              .map(new Func1<ServiceResponse<Page<CertificateIssuerItem>>, Page<CertificateIssuerItem>>() {
                  @Override
                  public Page<CertificateIssuerItem> call(ServiceResponse<Page<CertificateIssuerItem>> response) {
                      return response.body();
                  }
              });
      }
docs: List certificate issuers for a specified key vault.
  The GetCertificateIssuers operation returns the set of certificate issuer resources in the specified key vault. This operation requires the certificates/manageissuers/getissuers permission.
  
  @param nextPageLink The NextLink from the previous successful call to List operation.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the PagedList&lt;CertificateIssuerItem&gt; object