staff.md: Only include TAs if there are any TAs

staff.md

@@ -16,9 +16,12 @@ Staff information is stored in the `_staffers` directory and rendered according
 {{ staffer }}
 {% endfor %}
 
+{% assign teaching_assistants = site.staffers | where: 'role', 'Teaching Assistant' %}
+{% assign num_teaching_assistants = teaching_assistants | size %}
+{% if num_teaching_assistants != 0 %}
 ## Teaching Assistants
 
-{% assign teaching_assistants = site.staffers | where: 'role', 'Teaching Assistant' %}
 {% for staffer in teaching_assistants %}
 {{ staffer }}
 {% endfor %}
+{% endif %}