helm-do-ag not working as expected to search with command-option

Question

I want a function to search in filenames and retrieve those filenames containing the string I search for.

For some reason, this piece of code is not working for this purpose:

(defun helm-do-ag-projects ()
  "Grep string in Project directory" (interactive)
  (let ((rootdir (concat "~/my_projects/")))
    (let ((helm-ag-command-option (concat helm-ag-command-option "--all-text -g")))
      (helm-do-ag rootdir))))

When I run it, I get: