I was just curious of the proper way to set the default value to NONE when creating the date field via PHP code as follows. I have tried setting the default_value parameter to NULL and none without success:

<?php
$fields_array
= array(
        array(
           
'field' => array(
               
'field_name' => 'field_test_date',
               
'type' => 'datetime',
               
'cardinality' => 1,
               
'label' => 'Calendar',
               
'settings' => array(),
            ),
           
'instance' => array(
               
'field_name' => 'field_test_date',
               
'entity_type' => 'field_collection_item',
               
'bundle' => 'field_test_c',
               
'label' => 'Calendar',
               
'cardinality' => 1,
               
'description' => '',
               
'#default_value' => NULL,
               
'widget' => array(
                   
'type' => 'text_textfield',
                   
'weight' => 0,
                   
'settings' => array('size' => 50),
                ),
               
'display' => array(
                   
'default' => array(
                       
'label' => 'above',
                       
'settings' => array(),
                       
'weight' => 1,
                    ),
                   
'teaser' => array(
                       
'label' => 'above',
                       
'settings' => array(),
                       
'type' => 'hidden',
                    ),
                ),
               
'required' => FALSE,
            )
        ),
    );
?>