RegistryErrorExceptionBuilder addReason(String reason) {
    if (!firstErrorReason) {
      errorMessageBuilder.append(", ");
    }
    errorMessageBuilder.append(reason);
    firstErrorReason = false;
    return this;
  }
Adds an entry to the error reasons.
jib-core/src/main/java/com/google/cloud/tools/jib/registry/RegistryErrorExceptionBuilder.java