fix picture_path in template

templates/gspecies_compose.yml.j2

@@ -42,7 +42,7 @@ services:
             - ./banner.png:/var/www/html/banner.png:ro
             {% endif %}
             #- /groups/XXX/:/groups/XXX/:ro  # We do this when we have symlinks in src_data pointing to /groups/XXX/...
-            {% if 'picture_path' is defined %}
+            {% if 'picture_path' is defined and 'picture_path' != ''  %}
                 {% if 'png' in picture_path %}
             - ./species.png:/var/www/html/species.png:ro
                 {% endif %}