"Notice: Array to string conversion" of multicheck field in own field type

[eriktelepovsky]

I followed this example: https://github.com/WebDevStudios/CMB2/wiki/Adding-your-own-field-types#example-4-multiple-inputs-one-field-lets-create-an-address-field

Everything works fine until I change type of 'state' field from select to multicheck.

Expected Behavior:

Change select dropdown to multicheck checkboxes.

Actual Behavior:

It throws Notice: Array to string conversion in .../wp-content/plugins/cmb2/includes/types/CMB2_Type_Base.php on line 103

Steps to reproduce (I have confirmed I can reproduce this issue on the trunk branch):

Create custom field type address using this snippet:

https://github.com/WebDevStudios/CMB2-Snippet-Library/blob/master/custom-field-types/address-field-type.php

and change select to multicheck on line 134.

CMB2 Field Registration Code:

add_action( 'cmb2_admin_init', 'yourprefix_register_demo_metabox' );
function yourprefix_register_demo_metabox() {

	$cmb = new_cmb2_box( array(
		// Box Config...
	) );

	$cmb->add_field( array(
		// Field Config...
                'type' => 'address'
	) );
}

Thank you for any help.

Reference: CMB2/CMB2#801