docker: fix secrets thing?

app/docker/tls.sls

@@ -27,7 +27,7 @@
     - group: docker
     - mode: 0660
     - onlyif: "test ! -f {{ cert_file }}"
-{% if cert_data %}    - contents_pillar: "docker:tls:cert"
+{% if cert_data is not none %}    - contents_pillar: "docker:tls:cert"
 {% endif %}
 
 {{ key_file }}:
@@ -36,7 +36,7 @@
     - group: docker
     - mode: 0660
     - onlyif: "test ! -f {{ key_file }}"
-{% if key_data %}    - content_pillar: "docker:tls:key"
+{% if key_data is not none %}    - content_pillar: "docker:tls:key"
 {% endif %}
 
 {{ ca_file }}:
@@ -45,5 +45,5 @@
     - group: docker
     - mode: 0660
     - onlyif: "test ! -f {{ ca_file }}"
-{% if ca_data %}    - content_pillar: "docker:tls:ca"
+{% if ca_data is not none %}    - content_pillar: "docker:tls:ca"
 {% endif %}