Comment in REPL triggers an exception

[xitology]

In the current master, writing a bare comment in REPL triggers an exception, like this:

julia> # foo
ERROR: type Nothing has no field head
Stacktrace:
  [1] getproperty(x::Nothing, f::Symbol)
    @ Base ./Base.jl:33
  [2] modules_to_be_loaded(ast::Any, mods::Any) (repeats 2 times)
    @ REPL ~/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:178
  [3] check_for_missing_packages_and_run_hooks(ast::Any)
    @ REPL ~/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:168
  [4] eval_user_input(ast::Any, backend::REPL.REPLBackend)
    @ REPL ~/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:143
  [5] repl_backend_loop(backend::REPL.REPLBackend)
    @ REPL ~/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:237
  [6] start_repl_backend(backend::REPL.REPLBackend, consumer::Any)
    @ REPL ~/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:222
  [7] run_repl(repl::REPL.AbstractREPL, consumer::Any; backend_on_current_task::Bool)
    @ REPL ~/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:355
  [8] run_repl(repl::REPL.AbstractREPL, consumer::Any)
    @ REPL ~/src/julia/usr/share/julia/stdlib/v1.7/REPL/src/REPL.jl:342
  [9] (::Base.var"#892#894"{Bool, Bool, Bool})(REPL::Module)
    @ Base ./client.jl:394
 [10] #invokelatest#2
    @ ./essentials.jl:726 [inlined]
 [11] invokelatest
    @ ./essentials.jl:724 [inlined]
 [12] run_main_repl(interactive::Bool, quiet::Bool, banner::Bool, history_file::Bool, color_set::Bool)
    @ Base ./client.jl:379
 [13] exec_options(opts::Base.JLOptions)
    @ Base ./client.jl:309
 [14] _start()
    @ Base ./client.jl:495

julia> versioninfo()
Julia Version 1.7.0-DEV.1079
Commit e4f79b7167* (2021-05-10 15:38 UTC)
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-11.0.1 (ORCJIT, skylake)
Environment:
  JULIA_EDITOR = gvim

[oscardssmith]

Confirmed. This is one of the weirder bugs I've seen in a while.

[simeonschaub]

Looks like this was introduced in #39026.
cc @IanButterworth

[IanButterworth]

This is now fixed on the nightlies