Internal error parsing `+=`

[JeffBezanson]

julia> Meta.parse("+=")
┌ Error: JuliaSyntax parser failed — falling back to flisp!
│   exception =
│    MethodError: no method matching head(::Nothing)
│    
│    Closest candidates are:
│      head(::JuliaSyntax.GreenNode)
│       @ JuliaSyntax ~/.julia/dev/JuliaSyntax/sysimage/JuliaSyntax/src/green_tree.jl:69
│      head(::JuliaSyntax.SyntaxToken)
│       @ JuliaSyntax ~/.julia/dev/JuliaSyntax/sysimage/JuliaSyntax/src/parse_stream.jl:127
│      head(::JuliaSyntax.TaggedRange)
│       @ JuliaSyntax ~/.julia/dev/JuliaSyntax/sysimage/JuliaSyntax/src/parse_stream.jl:146
│      ...
│    
│    Stacktrace:
│      [1] kind(x::Nothing)
│        @ JuliaSyntax ~/.julia/dev/JuliaSyntax/sysimage/JuliaSyntax/src/parse_stream.jl:91
│      [2] _incomplete_tag(n::JuliaSyntax.SyntaxNode)
│        @ JuliaSyntax ~/.julia/dev/JuliaSyntax/sysimage/JuliaSyntax/src/hooks.jl:55
│      [3] _core_parser_hook(code::String, filename::String, lineno::Int64, offset::Int64, options::Symbol)
│        @ JuliaSyntax ~/.julia/dev/JuliaSyntax/sysimage/JuliaSyntax/src/hooks.jl:172