Include In Rotator option in Media Uploader

gistfile1.php

<?php


/**
 * Add "Include in Rotator" option to media uploader
 * Limited to Home page
 *
 * @param $form_fields array, fields to include in attachment form
 * @param $post object, attachment record in database
 * @return $form_fields, modified form fields
 */
 
function be_attachment_field_rotator( $form_fields, $post ) {

//  // Only show on front page
	if( ! ( $post->post_parent == get_option( 'page_on_front' ) ) )
		return $form_fields;

	// Set up options
	$options = array( '1' => 'Yes', '0' => 'No' );
	
	// Get currently selected value
	$selected = get_post_meta( $post->ID, 'be_rotator_include', true );
	
	// If no selected value, default to 'No'
	if( !isset( $selected ) ) 
		$selected = '0';
	
	// Display each option	
	foreach ( $options as $value => $label ) {
		$checked = '';
		$css_id = 'rotator-include-option-' . $value;

		if ( $selected == $value ) {
			$checked = " checked='checked'";
		}

		$html = "<div class='rotator-include-option'><input type='radio' name='attachments[$post->ID][be-rotator-include]' id='{$css_id}' value='{$value}'$checked />";

		$html .= "<label for='{$css_id}'>$label</label>";

		$html .= '</div>';

		$out[] = $html;
	}

	// Construct the form field
	$form_fields['be-include-rotator'] = array(
		'label' => 'Include in Rotator',
		'input' => 'html',
		'html'  => join("\n", $out),
	);
	
	// Return all form fields
	return $form_fields;
}

add_filter( 'attachment_fields_to_edit', 'be_attachment_field_rotator', 10, 2 );


/**
 * Save value of "Include in Rotator" selection in media uploader
 *
 * @param $post array, the post data for database
 * @param $attachment array, attachment fields from $_POST form
 * @return $post array, modified post data
 */
 
function be_attachment_field_rotator_save( $post, $attachment ) {
	if( isset( $attachment['be-rotator-include'] ) ) 
		update_post_meta( $post['ID'], 'be_rotator_include', $attachment['be-rotator-include'] );
	
	return $post;
}

add_filter( 'attachment_fields_to_save', 'be_attachment_field_rotator_save', 10, 2 );

I'm pretty sure if( !isset( $selected ) ) (line 31 right now) will always return false, since get_post_meta() "returns an empty string if the key has not been set yet" (http://codex.wordpress.org/Function_Reference/get_post_meta#Return_Value).

Looks like if( '' == $selected ) would work, since the only way the value of $selected should be an empty string is if postmeta for this key hasn't been set yet. Note that using empty() doesn't work, since that returns true if passed an integer 0, a float 0.0, or a string '0'.

I should note that I only ran into an issue when I used this code but changed the keys in the $options array. I'm honestly a little confused about why it works as posted, though.