Exit with zero datapoints message if no datapoints exist (#43)

* Exit with zero datapoints message if no datapoints exist

lib/sensu-plugins-graphite/graphite_proxy/proxy.rb

@@ -3,10 +3,7 @@
 module SensuPluginsGraphite
   module GraphiteProxy
     class ProxyError < StandardError
-      attr_accessor :exception
-
-      def initialize(msg, args)
-        self.exception = args[:exception]
+      def initialize(msg)
         super msg
       end
     end
@@ -87,24 +84,20 @@ def retrieve_data!
             handle = open(url, request_auth_options(config))
 
             @raw_data = handle.gets
-            if @raw_data == '[]'
-              unknown 'Empty data received from Graphite - metric probably doesn\'t exists'
-            else
-              json_data = JSON.parse(@raw_data)
-              format_output(json_data)
-            end
-          rescue OpenURI::HTTPError => e
-            raise ProxyError.new('Failed to connect to Graphite server', exception: e)
-          rescue NoMethodError => e
-            raise ProxyError.new('No data for time period and/or target', exception: e)
-          rescue Errno::ECONNREFUSED => e
-            raise ProxyError.new('Connection refused when connecting to Graphite server', exception: e)
-          rescue Errno::ECONNRESET => e
-            raise ProxyError.new('Connection reset by peer when connecting to Graphite server', exception: e)
-          rescue EOFError => e
-            raise ProxyError.new('End of file error when reading from Graphite server', exception: e)
+            json_data = JSON.parse(@raw_data)
+            format_output(json_data)
+          rescue OpenURI::HTTPError
+            raise ProxyError, 'Failed to connect to Graphite server'
+          rescue NoMethodError, JSON::ParserError
+            raise ProxyError, 'No data for time period and/or target'
+          rescue Errno::ECONNREFUSED
+            raise ProxyError, 'Connection refused when connecting to Graphite server'
+          rescue Errno::ECONNRESET
+            raise ProxyError, 'Connection reset by peer when connecting to Graphite server'
+          rescue EOFError
+            raise ProxyError, 'End of file error when reading from Graphite server'
           rescue => e
-            raise ProxyError.new("An unknown error occurred: #{e.inspect}", exception: e)
+            raise ProxyError, "An unknown error occurred: #{e.inspect}"
           end
         end
       end