Indentation after parens produces unwanted completion

[debug-ito]

I use elm-mode-0.21.0 on Emacs 25.2.2 (Linux).

Steps to reproduce

1. Type the following.

let foo = [
          ]

2. Set the cursor at the beginning of the line just after ']'.
3. Hit TAB.
4. Then, it produces

let foo = [
          ]
    foo 

What's this completion of foo? I don't need it.

Exepectation

I just want to indent it to the column of the head of "foo" (the best)

let foo = [
          ]
....

or, I want it to align to the previous indentation (the second best)

let foo = [
          ]
..........