`attempt to call field 'nvim_get_hl' (a nil value)` when calling `setup`

[mawkler]

Since a couple of days ago I started getting this error when calling require('diffview).setup({}):

Error executing Lua callback: ...ig/nvim/.repro/plugins/diffview.nvim/lua/diffview/hl.lua:129: attempt to call field 'nvim_get_hl' (a nil value)
stack traceback:
        ...ig/nvim/.repro/plugins/diffview.nvim/lua/diffview/hl.lua:129: in function 'get_hl'
        ...ig/nvim/.repro/plugins/diffview.nvim/lua/diffview/hl.lua:166: in function 'get_hl_attr'
        ...ig/nvim/.repro/plugins/diffview.nvim/lua/diffview/hl.lua:185: in function 'get_fg'
        ...ig/nvim/.repro/plugins/diffview.nvim/lua/diffview/hl.lua:466: in function 'update_diff_hl'
        ...ig/nvim/.repro/plugins/diffview.nvim/lua/diffview/hl.lua:475: in function 'setup'
        .../nvim/.repro/plugins/diffview.nvim/lua/diffview/init.lua:25: in function 'init'
        .../nvim/.repro/plugins/diffview.nvim/lua/diffview/init.lua:260: in main chunk
        [C]: in function 'handler'
        .../nvim/.repro/plugins/diffview.nvim/lua/diffview/lazy.lua:21: in function '__get'
        .../nvim/.repro/plugins/diffview.nvim/lua/diffview/lazy.lua:36: in function '__index'
        ...ig/nvim/.repro/plugins/diffview.nvim/plugin/diffview.lua:24: in function <...ig/nvim/.repro/plugins/diffview.nvim/plugin/diffview.lua:23>

Here's the minimal lazy.nvim config that I'm using:

{
  'sindrets/diffview.nvim',
  dependencies = 'nvim-lua/plenary.nvim',
  config = function()
    require('diffview').setup({})
  end
}

[sindrets]

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