"code_string" doesn't work in Documenter.jl and JupyterNotebook environment

[bennibolm]

When calling

f(x) = x
code_string(f, (Float64,))

in a Documenter.jl setup, I get the error MethodError: no method matching getindex(::Nothing, ::Int64).

The same happens when I call code_string in JupyterNotebook:

In the REPL, it works perfectly. Is that a known bug? It seems to be similar to #51.

[KristofferC]

Yeah, it is pretty much the same as #51. You can add this comment there.