public Optional<String> getToCredentialHelper() {
    if (credentials != null
        && credentials.separate != null
        && credentials.separate.to != null
        && credentials.separate.to.credentialHelper != null) {
      return Optional.of(credentials.separate.to.credentialHelper);
    }
    return Optional.empty();
  }
Returns the user configured credential helper for the target image registry, this can be
interpreted as a path or a string.

@return a Optional string reference to the credential helper
jib-cli/src/main/java/com/google/cloud/tools/jib/cli/CommonCliOptions.java