Better parsing of layout files

Handles empty rules and empty files better now.

Fixes #14

lib/squib/deck.rb

@@ -115,7 +115,7 @@ module Squib
         thefile = file
         thefile = "#{File.dirname(__FILE__)}/layouts/#{file}" unless File.exists?(file)
         if File.exists? thefile
-          yml = @layout.merge(YAML.load_file(thefile))
+          yml = @layout.merge(YAML.load_file(thefile) || {}) #load_file returns false on empty file
           yml.each do |key, value|
             @layout[key] = recurse_extends(yml, key, {})
           end
@@ -157,7 +157,7 @@ module Squib
     # :nodoc:
     # @api private
     def has_extends?(yml, key)
-      yml[key].key?('extends')
+      !!yml[key] && yml[key].key?('extends')
     end
 
     # Safeguard against malformed circular extends

spec/data/layouts/empty-rule.yml

@@ -0,0 +1 @@
+empty: #no rules actually set

spec/data/layouts/empty.yml

@@ -0,0 +1 @@
+# testing for an empty yaml file here

spec/deck_spec.rb

@@ -207,6 +207,18 @@ describe Squib::Deck do
           })
     end
 
+    it 'loads nothing on an empty layout file' do
+      d = Squib::Deck.new(layout: layout_file('empty.yml'))
+      expect(d.layout).to eq({})
+    end
+
+    it 'handles extends on a rule with no args' do
+      d = Squib::Deck.new(layout: layout_file('empty-rule.yml'))
+      expect(d.layout).to eq({
+        'empty' => nil
+      })
+    end
+
   end
 
 end