@Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("{");
        if (getPayloadFormatIndicator() != null)
            sb.append("PayloadFormatIndicator: ").append(getPayloadFormatIndicator()).append(",");
        if (getContentType() != null)
            sb.append("ContentType: ").append(getContentType()).append(",");
        if (getResponseTopic() != null)
            sb.append("ResponseTopic: ").append(getResponseTopic()).append(",");
        if (getCorrelationData() != null)
            sb.append("CorrelationData: ").append(getCorrelationData()).append(",");
        if (getMessageExpiry() != null)
            sb.append("MessageExpiry: ").append(getMessageExpiry()).append(",");
        if (getUserProperties() != null)
            sb.append("UserProperties: ").append(getUserProperties());
        sb.append("}");
        return sb.toString();
    }
Returns a string representation of this object. This is useful for testing and debugging. Sensitive data will be
redacted from this string using a placeholder value.

@return A string representation of this object.

@see java.lang.Object#toString()
aws-java-sdk-iot/src/main/java/com/amazonaws/services/iot/model/MqttHeaders.java