private String getTextField(JsonNode json, String fieldName) {
        if (!json.has(fieldName)) {
            return null;
        }
        return json.get(fieldName).asText();
    }
Get a String field from the JSON.

@param json      JSON document.
@param fieldName Field name to get.
@return String value of field or null if not present.
aws-java-sdk-kinesisvideo/src/main/java/com/amazonaws/services/kinesisvideo/model/transform/AckEventUnmarshaller.java