NPE calling Orm#value on a new resource.

[jcoyne]

 res = Ldp::Resource::RdfSource.new(FedoraLens.connection, '/foobara')
=> #<Ldp::Resource::RdfSource:0x007fdc75020e28 @client=#<Ldp::Client:0x007fdc737ca838 @http=#<Faraday::Connection:0x007fdc737ca680 @parallel_manager=nil, @headers={"User-Agent"=>"Faraday v0.9.0"}, @params={}, @options=#<Faraday::RequestOptions (empty)>, @ssl=#<Faraday::SSLOptions (empty)>, @default_parallel_manager=nil, @builder=#<Faraday::RackBuilder:0x007fdc737ca180 @handlers=[Faraday::Request::UrlEncoded, Faraday::Adapter::NetHttp]>, @url_prefix=#<URI::HTTP:0x007fdc75023e20 URL:http://localhost:8983/fedora/rest>, @proxy=nil>>, @subject="/foobara">
irb(main):003:0> orm = Ldp::Orm.new(res)
=> #<Ldp::Orm:0x007fdc750a0f10 @resource=#<Ldp::Resource::RdfSource:0x007fdc75020e28 @client=#<Ldp::Client:0x007fdc737ca838 @http=#<Faraday::Connection:0x007fdc737ca680 @parallel_manager=nil, @headers={"User-Agent"=>"Faraday v0.9.0"}, @params={}, @options=#<Faraday::RequestOptions (empty)>, @ssl=#<Faraday::SSLOptions (empty)>, @default_parallel_manager=nil, @builder=#<Faraday::RackBuilder:0x007fdc737ca180 @handlers=[Faraday::Request::UrlEncoded, Faraday::Adapter::NetHttp]>, @url_prefix=#<URI::HTTP:0x007fdc75023e20 URL:http://localhost:8983/fedora/rest>, @proxy=nil>>, @subject="/foobara">>
irb(main):004:0> orm.value('foo')
NoMethodError: undefined method `query' for nil:NilClass
    from /Users/justin/workspace/ldp/lib/ldp/orm.rb:22:in `value'
    from (irb):4