"undefined method `&'" error

I get the following error when trying to use the fluentd riemann plugin.

2015-07-14 11:49:29 +0100 [warn]: temporarily failed to flush the buffer. next_retry=2015-07-14 11:49:30 +0100 error_class="NoMethodError" error="undefined method &' for 1436870957.640452:Float" plugin_id="object:f581b0" 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake/buffer/encode.rb:86:inappend_uint64' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake/buffer/encode.rb:61:in append_int64' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake/buffer/encode.rb:13:inappend' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:126:in block in encode!' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:114:ineach' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:114:in encode!' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:103:inblock in encode' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:96:in each' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:96:inencode' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:118:in block in encode!' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:114:ineach' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:114:in encode!' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:103:inblock in encode' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:96:in each' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/beefcake-1.1.0/lib/beefcake.rb:96:inencode' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/riemann-client-0.2.5/lib/riemann/message.rb:12:in encode_with_length' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/riemann-client-0.2.5/lib/riemann/client/tcp.rb:78:inblock in send_recv' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/riemann-client-0.2.5/lib/riemann/client/tcp.rb:92:in block in with_connection' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/2.1.0/monitor.rb:211:inmon_synchronize' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/riemann-client-0.2.5/lib/riemann/client/tcp.rb:89:in with_connection' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/riemann-client-0.2.5/lib/riemann/client/tcp.rb:77:insend_recv' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/riemann-client-0.2.5/lib/riemann/client.rb:63:in <<' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/fluent-plugin-riemann-0.0.3/lib/fluent/plugin/out_riemann.rb:61:inblock in write' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/fluentd-0.12.12/lib/fluent/plugin/buf_memory.rb:61:in feed_each' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/fluentd-0.12.12/lib/fluent/plugin/buf_memory.rb:61:inmsgpack_each' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/fluent-plugin-riemann-0.0.3/lib/fluent/plugin/out_riemann.rb:51:in write' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/fluentd-0.12.12/lib/fluent/buffer.rb:325:inwrite_chunk' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/fluentd-0.12.12/lib/fluent/buffer.rb:304:in pop' 2015-07-14 11:49:29 +0100 [warn]: /opt/td-agent/embedded/lib/ruby/gems/2.1.0/gems/fluentd-0.12.12/lib/fluent/output.rb:321:intry_flush'

config:

type riemann host btn-docker-03 #port 5555 timeout 60 protocol tcp service logs fields message:description,level:state types metric:float flush_interval 10s

td-agent version: 0.12.12

wkf / fluent-plugin-riemann

"undefined method `&'" error #3