WP Customizer - Section Settings to Front End

Not sure how to phrase the question exactly but I am working on adding custom items to the theme customizer in Wordpress.

I have added a Section for the user to add Social Media Accounts and have a linked image show if content exists.  Here is my code in my functions file.

// add Social Media Selction section
	$wp_customize->add_section( 'parallaxone_social_options_section' , array(
		'title'      => __( 'Social Media Options', 'parallaxone' ),
		'priority'   => 150,
	) );	
	// add setting to select facebook
	$wp_customize->add_setting( 'parallaxone_facebook_select', array( 
		'fbdefault' 	=> ' '
	) );
		$wp_customize->add_control( 'parallaxone_facebook_select', array(
		'label'     => __( 'Facebook', 'parallaxone' ),
		'section'   => 'parallaxone_social_options_section',
		'priority'  => 10,
		'type'      => 'text'
	) );
	
	// add setting to select twitter
	$wp_customize->add_setting( 'parallaxone_twitter_select', array( 
		'twdefault' 	=> ' '
	) );
		$wp_customize->add_control( 'parallaxone_twitter_select', array(
		'label'     => __( 'Twitter', 'parallaxone' ),
		'section'   => 'parallaxone_social_options_section',
		'priority'  => 20,
		'type'      => 'text'
	) );

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And here is my front end code on the home page;

<?php $fbdef = get_theme_mod( 'parallaxone_facebook_select', $fbdefault);
					if ($fbdef !== $fbdefault) { ?>
					<img src="<?php bloginfo('template_directory'); ?>/images/social/facebook-social.png" />
                    <?php } ?>	
                    
					<?php $twdef = get_theme_mod( 'parallaxone_twitter_select', $twdefault);
					if ($twdef !== $twdefault) { ?>
					<a href="http://www.twitter.com/<?php echo $twdef; ?>"><img src="<?php bloginfo('template_directory'); ?>/images/social/twitter-social.png" /></a>
                    <?php echo $twdefault; ?>
                    <?php } ?>

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Basically, what I want to happen is for the social media image to only show if there is a value given by the user.  It works fine for the FB setting and control, but doesn't seem to work for the Twitter Setting and Control.  It shows if either is active. and a blank text box doesn't seem to reset the default to ' ',

I think that is the issue here, but not sure how to reset the text value when no data is provided.