Generic avatar appear if author doesn’t have gravatar

Hi,

I’m developing a website with about 120 authors, each with their own page. As you can imagine a fair few haven’t uploaded gravatar images to their email so at the moment there’s an empty image on their author page. I’d like to set up a statement that says:

if author has gravatar display gravatar
else if author doesn’t have gravatar show generic avatar

I’ve copied the code I’m using below. The problem is that the get_avatar function always exists because gravatar.com appears to create a gravatar image using a string of numbers relating to the author email regardless of whether it exists or not (e.g. <img src=”https://www.gravatar.com/avatar/e421fe9c8a99f1812ec6e38a84c27a7f?s=100&d=%23646464&r=G”&gt;)

An example of an author page, w/out an image on, that I’m talking about is here: https://www.climatemediapartnership.org/author/annabel_fuller/

The code is below:

<p>	<?php
if(isset($_GET['author_name'])) :
$curauth = get_userdatabylogin($author_name);
else : $curauth = get_userdata(intval($author));
endif;
?>

<h2> <?php echo $curauth->display_name; ?></h2>
	<?php global $authordata, $curauth;
		$authordata=get_userdata(get_query_var( 'author' )); if(function_exists('get_avatar')) { echo get_avatar( get_the_author_id(), 100, "#646464", $default = '' ); }
else { echo '<img src="https://www.climatemediapartnership.org/wp-content/themes/ccmp-style/img/avatar.gif" width="100" height="100" />'; } ?>
<p><?php echo $curauth->user_description; ?></p>
<div style="clear: both"></div>

Any help would be gratefully received!!
thanks alot,
edd