Cannot load empty YAML file

[Paalon]

The following gives an error:

using YAML

YAML.load("")

ERROR: AssertionError: typeof(forward!(composer.input)) == DocumentStartEvent
Stacktrace:
 [1] compose_document(composer::YAML.Composer)
   @ YAML ~/.julia/packages/YAML/U6OOW/src/composer.jl:49
 [2] compose(events::YAML.EventStream)
   @ YAML ~/.julia/packages/YAML/U6OOW/src/composer.jl:38
 [3] load(ts::YAML.TokenStream, constructor::YAML.Constructor)
   @ YAML ~/.julia/packages/YAML/U6OOW/src/YAML.jl:38
 [4] load(ts::YAML.TokenStream, more_constructors::Nothing, multi_constructors::Dict{…}; dicttype::Type{…}, constructorType::typeof(YAML.SafeConstructor))
   @ YAML ~/.julia/packages/YAML/U6OOW/src/YAML.jl:44
 [5] load
   @ ~/.julia/packages/YAML/U6OOW/src/YAML.jl:44 [inlined]
 [6] load (repeats 3 times)
   @ ~/.julia/packages/YAML/U6OOW/src/YAML.jl:47 [inlined]
 [7] load(::String)
   @ YAML ~/.julia/packages/YAML/U6OOW/src/YAML.jl:88
 [8] top-level scope
   @ REPL[8]:1
Some type information was truncated. Use `show(err)` to see complete types.

Empty YAML file is a valid YAML file.

[Paalon]

Maybe same reason to #129

[Paalon]

Result of empty YAML from YPaste Interactive Parser:

[Paalon]

I noticed that this is not a bug because we can't get first document from 0 documents. It's same as [][begin] gives BoundsError in Julia. However this is not user-friendly API name. See #145.

[GunnarFarneback]

The error is of course accidental and not helpful at all. But the user-friendly solution would be to just return a nothing for a file without a document.

[GunnarFarneback]

Regardless of the philosophy around load of a file with no document, this shouldn't error:

julia> YAML.load_all("#")
ERROR: AssertionError: forward!(composer.input) isa DocumentStartEvent