Support legacy heka.server without parse error
diff --git a/heka/server.sls b/heka/server.sls
index c2de1a0..888f04c 100644
--- a/heka/server.sls
+++ b/heka/server.sls
@@ -1,5 +1,5 @@
 {%- from "heka/map.jinja" import server with context %}
-{%- if server.enabled %}
+{%- if server.enabled is defined and server.enabled %}
 
 heka_packages:
   pkg.latest:
@@ -198,4 +198,4 @@
 {%- endif %}
 {%- endfor %}
 
-{%- endif %}
\ No newline at end of file
+{%- endif %}