vlib/v/checker/tests/option_var_unwrap_err.vv:5:9: error: to propagate the Option, `abc_2` must return an Option type
    3 | 
    4 | fn abc_2(a ?string) string {
    5 |     return a?
      |            ^
    6 | }
    7 |
Details: vlib/v/checker/tests/option_var_unwrap_err.vv:4:21: details: prepend ? before the declaration of the return type of `abc_2`
    2 | }
    3 | 
    4 | fn abc_2(a ?string) string {
      |                     ~~~~~~
    5 |     return a?
    6 | }
vlib/v/checker/tests/option_var_unwrap_err.vv:5:2: error: should not unwrap option var on return, it could be none
    3 | 
    4 | fn abc_2(a ?string) string {
    5 |     return a?
      |     ~~~~~~~~
    6 | }
    7 |