Ex_doc CLI use problem

Hi! I try to follow ex_doc README - the part of CLI using. So I have cloned ex_doc and ecto. After compiling of both apps I try to generate a doc:

$ ../ex_doc/bin/ex_doc "Ecto" "master" _build/shared/lib/ecto/ebin/
** (FunctionClauseError) no function clause matching in Keyword.keys/1
    (elixir) lib/keyword.ex:373: Keyword.keys(nil)
    lib/ex_doc/retriever.ex:398: anonymous fn/2 in ExDoc.Retriever.get_impls/1
    (elixir) lib/enum.ex:1623: Enum."-reduce/3-lists^foldl/2-0-"/3
    lib/ex_doc/retriever.ex:149: ExDoc.Retriever.generate_node/3
    (elixir) lib/enum.ex:1184: Enum."-map/2-lists^map/1-0-"/2
    (elixir) lib/enum.ex:1184: Enum."-map/2-lists^map/1-0-"/2
    lib/ex_doc/retriever.ex:101: ExDoc.Retriever.docs_from_modules/2
    lib/ex_doc.ex:68: ExDoc.generate_docs/3

Where to go further to get thing done?

Try running MIX_ENV=docs mix docs for generating docs inside the Ecto project. I will investigate why your particular invocation does not work.

The commands ends up without any problems:

$ MIX_ENV=docs mix docs
==> earmark
Compiling 1 file (.erl)
Compiling 16 files (.ex)
warning: variable pending_lnb is unused

warning: unused import Earmark.Helpers.StringHelpers

Generated earmark app
==> ex_doc
Compiling 12 files (.ex)
Generated ex_doc app
==> inch_ex
Compiling 15 files (.ex)
Generated inch_ex app
==> ecto
Compiling 67 files (.ex)
Generated ecto app
Docs successfully generated.
View them at "doc/index.html".

Probably I must clarify my initial intention. I have tried to use CLI with the aim to check EPUB formatter.

I guess I must inform the current ex_doc version (master HEAD) does work for me - have generated docs (EPUB also) for Ecto and Plug from CLI.