Template Error

Impossible to access an attribute ("firstName") on a null variable.

/home2/medialandscapes/craft/templates/authors/_entry.html(8)

01 {% set entryName =  craft.request.getSegment(2) %}
02 {% set author = craft.users.group('authors').lastName(entryName).first() %}
03 
04 {% extends "_layout" %}
05 
06 
07 {% do craft.sproutSeo.meta({
08     title: author.firstName ~ " " ~ author.lastName ~ " - Author",
09     description: author.authorBiographyIntroduction,
10 }) %}
11 
12 
13 
14 {% block content %}
15     <div class="breadcrumbs">
16         <div class="container">
17             <div class="row">
18                 <div class="col-xs-12">
19                     <ul>
20                         <li>
2024-03-28 10:13:51 Apache / Craft CMS 2.9.2