Impossible to invoke a method ("focusCrop") on a null variable.
<div class="team">
{% for team_member in page.team_members.toStructure %}
<div class="team-member">
{% set picture = page.image(team_member.picture.yaml[0]) %}
<figure class="team-member__photo">
<img
srcset="{{ picture.focusCrop(1170, 832).url }} 1170w, {{ picture.focusCrop(585, 416).url }} 585w"
sizes="585px"
src="{{ picture.focusCrop(1170, 832).url }}"
alt="{{ team_member.name }}"
title="{{ team_member.name }}">
</figure>
<div class="team-member__description">