strange error

gistfile1.txt

Erlang R14A (erts-5.8) [source] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8  (abort with ^G)
1> P = [{filename,"Filename"},
1>  {maintainer,"Maintainer"},
1>  {description,"Description"},
1>  {package,"Package"},
1>  {section,"Section"},
1>  {'installed-size',"Installed-Size"},
1>  {priority,"Priority"},
1>  {suggests,"Suggests"},
1>  {depends,"Depends"},
1>  {version,"Version"},
1>  {source,"Source"},
1>  {architecture,"Architecture"}].
[{filename,"Filename"},
 {maintainer,"Maintainer"},
 {description,"Description"},
 {package,"Package"},
 {section,"Section"},
 {'installed-size',"Installed-Size"},
 {priority,"Priority"},
 {suggests,"Suggests"},
 {depends,"Depends"},
 {version,"Version"},
 {source,"Source"},
 {architecture,"Architecture"}]
2> T = gb_trees:from_orddict(P).
{12,
 {priority,"Priority",
           {package,"Package",
                    {maintainer,"Maintainer",
                                {filename,"Filename",nil,nil},
                                {description,"Description",nil,nil}},
                    {'installed-size',"Installed-Size",
                                      {section,"Section",nil,nil},
                                      nil}},
           {version,"Version",
                    {depends,"Depends",{suggests,"Suggests",nil,nil},nil},
                    {architecture,"Architecture",
                                  {source,"Source",nil,nil},
                                  nil}}}}
3> gb_trees:get(description, T).
** exception error: no function clause matching gb_trees:get_1(description,nil)
4> gb_trees:lookup(description, T).
none