How do you send an explicit null value using FuelSDK?

Question

I am using FuelSDK to send triggered emails using Salesforce Marketing Cloud (formerly ExactTarget). Here is an approximation of the code I'm using:

$triggeredsend = new ET_TriggeredSend();
$triggeredsend->authStub = $My_ET_Client;
$triggeredsend->props = array("CustomerKey" => 'MyTriggeredEmailID');
$triggeredsend->subscribers = array(
        array(
                "EmailAddress"  =>  '[email protected]', 
                "SubscriberKey" => $subscriber_key, 
                "Attributes" => $some_attributes));
$results = $triggeredsend->send();

Amidst $some_attributes in my example is a Date type field (we'll call it My_Date) that contains a null value. However, I get this response from SFMC:

Error Code: 20 - Value provided for My_Date cannot be stored in a Date field.

I see that if I were using SoapClient, I "must explicitly state that null value using the NullAPIProperty type":

https://code.exacttarget.com/apis-sdks/soap-api/updating-a-data-extension-object-with-a-null-field-value.html

How do I send a NullAPIProperty type attribute using FuelSDK?

Thanks in advance,

Ben

EDIT: Here is a more complete dump of the query and results. To further address Mark's proposed answer: This code is meant to trigger a TriggeredSend and send the appropriate subscriber information. You'll see that one of the fields -- the one that is causing the error message -- needs to have a null value. The field itself is already nullable. This operation is distinct from updating the DataExtension field itself.

DEBUG - 2016-01-06 21:01:30 --> Preparing to send triggers...
DEBUG - 2016-01-06 21:01:31 --> ET_Post Object
(
    [status] => 
    [code] => 200
    [message] => 
    [results] => Array
        (
            [0] => stdClass Object
                (
                    [StatusCode] => Error
                    [StatusMessage] => Unable to queue Triggered Send request.  There are no valid subscribers.
                    [OrdinalID] => 0
                    [ErrorCode] => 180008
                    [NewID] => 0
                    [SubscriberFailures] => stdClass Object
                        (
                            [Subscriber] => stdClass Object
                                (
                                    [PartnerKey] => 
                                    [ObjectID] => 
                                    [EmailAddress] => [email protected]
                                    [Attributes] => Array
                                        (
                                            [0] => stdClass Object
                                                (
                                                    [Name] => UserID
                                                    [Value] => 79
                                                )


                                        REDACTED

                                        [22] => stdClass Object
                                            (
                                                [Name] => Purchase_Date
                                                [Value] => 
                                            )

                                        REDACTED
                                    )

                                [SubscriberKey] => dev_79
                            )

                        [ErrorCode] => TriggeredSendSubscriberProcessingError
                        [ErrorDescription] => Error Code: 20 - Value provided for Purchase_Date cannot be stored in a Date field.
                    )

            )

    )

[request_id] => 
[moreResults] => 


)

Answer 1

Your question is specifically about the PHP FuelSDK, which I'm completely unfamiliar with so this is a shot in the dark.

It looks like you'll need to define an array specifically for the field that you're trying to null and add it to the collection.

$triggeredsend->subscribers = array(
        array(
                "EmailAddress"  =>  '[email protected]', 
                "SubscriberKey" => $subscriber_key, 
                "Attributes" => $some_attributes,
                "SendableDataExtensionField" => array(
                    'Name' => 'My_Date',
                    'Value' => NULL
                )
            )
        );

Syntax information gleaned from here: http://howtoforge.answers.sc/salesforce/questions/33999/fuel-sdk-php-sendable-data-extension.html

Answer 2

PHP has a NULL value that you can set nullable variables to, have you tried setting this attribute value to that? The example that you referenced above is for a .Net implementation, which is different than what your code is here.

$My_Date = NULL

When you say that the field is "Nullable" do you mean that the field is not required? Data Extension objects appear to have a IsRequired field by default. This apparently determines if a value has to be supplied or not.

Where is $some_attributes created?