on_attach not called for stylua when using handlers

[MartyMcFlyInTheSky]

I wanted to setup a handler for registering stylua with the current buffer. So I thought I could use my preexisting on_attach function that I use for my lsp's (is that a good idea?). Anyway, it doesn't seem to work, on_attach is not called. For this contrived example I replaced it with a more simple function that notifies me if stylua was attached:

...
    {
        "jay-babu/mason-null-ls.nvim",
        event = { "BufReadPre", "BufNewFile" },
        cmd = { "NullLsInstall", "NoneLsInstall", "NullLsUninstall", "NoneLsUninstall" },
        dependencies = {
            "williamboman/mason.nvim",
            "nvimtools/none-ls.nvim",
        },
        opts = {
            ensure_installed = {
                "black", "isort", "mypy",
                "stylua",
                "shftm",
                "clang_format",
            },
            automatic_installation = false,
            handlers = {
                function(source_name, methods)
                    vim.notify("Setting up Null LS for " .. source_name)
                    local null_ls = require("null-ls")
                    null_ls.register(null_ls.builtins.formatting.stylua.with({
                        on_attach = function() vim.notify("Attaching stylua") end,
                    }))
                end
            },
        },
    }
}

Am I doing this correctly, or what am I missing?

(I'm using lazy.nvim without a distro)

[MartyMcFlyInTheSky]

Oh I'm stupid, I thought you could have individual on_attach functions for all the formatters/diagnostics. I put the on_attach key into the direct mason-null-ls opts and that seems to work.