Change proxy Jinja logic (none and empty string are falsy)

salt/yum/etc/yum.conf.jinja

@@ -14,6 +14,6 @@ distroverpkg=centos-release
 clean_requirements_on_remove=1
 {% if (grains['role'] not in ['so-eval','so-managersearch', 'so-manager', 'so-standalone']) and salt['pillar.get']('global:managerupdate', '0') -%}
 proxy=http://{{ salt['pillar.get']('yum:config:proxy', salt['config.get']('master')) }}:3142
-{% elif proxy != '' and proxy is not none -%}
+{% elif proxy -%}
 proxy={{ proxy }}
 {% endif %}