Crashes if yaml file contains only a comment

[OmegaLambda1998]

Given the yaml file:

# Test

The following code crashes:

using YAML
open("test.yaml", "r") do io
    YAML.load(io)
end

With the error:

ERROR: AssertionError: typeof(forward!(composer.input)) == DocumentStartEvent
Stacktrace:
  [1] compose_document(composer::YAML.Composer)
    @ YAML ~/.julia/packages/YAML/78yP9/src/composer.jl:49
  [2] compose(events::YAML.EventStream)
    @ YAML ~/.julia/packages/YAML/78yP9/src/composer.jl:38
  [3] load(ts::YAML.TokenStream, constructor::YAML.Constructor)
    @ YAML ~/.julia/packages/YAML/78yP9/src/YAML.jl:38
  [4] load(ts::YAML.TokenStream, more_constructors::Nothing, multi_constructors::Dict{Any, Any}; dicttype::Type{Dict{Any, Any}}, constructorType::typeof(YAML.SafeConstructor))
    @ YAML ~/.julia/packages/YAML/78yP9/src/YAML.jl:44
  [5] load
    @ ~/.julia/packages/YAML/78yP9/src/YAML.jl:44 [inlined]
  [6] #load#10
    @ ~/.julia/packages/YAML/78yP9/src/YAML.jl:47 [inlined]
  [7] load (repeats 3 times)
    @ ~/.julia/packages/YAML/78yP9/src/YAML.jl:47 [inlined]
  [8] #load#13
    @ ~/.julia/packages/YAML/78yP9/src/YAML.jl:88 [inlined]
  [9] load(::String)
    @ YAML ~/.julia/packages/YAML/78yP9/src/YAML.jl:88
 [10] top-level scope
    @ REPL[7]:1

You can get an even quicker crash via:

YAML.load("#")

[OmegaLambda1998]

I'd expect this to return an empty dictionary, rather than crashing

[kescobo]

It's valid YAML according to https://www.yamllint.com/

[Paalon]

Result from YPaste Interactive Parser.

I think this should not return an empty dictionary because it's different.

[Paalon]

This YAML file # represents no document (0 documents).

[Paalon]

This is not a bug for the same reason as #143. But this is hard to notice that this is intentional.

[GunnarFarneback]

This crash was never intentional. #219 fixed it to return nothing. Returning an empty dictionary is indeed not an option.