Take multiple ACF user fields and combine them into one - wordpress

Question

I have some ACF user fields on posts where users can be selected, I would like to take those fields and combine them into another field. So basically the users in field 1 and field 2 show up in field 3. Here is what I have tried so far. The return format for the fields is user array.
add_action( 'acf/save_post',
'my_acf_save_post', 10 );
function my_acf_save_post( $post_id ) {
// Get value of field 1
$value1 = get_field( 'contractor',
$post_id );
// Get value of field 2
$value2 = get_field( 'architect',
$post_id );
update_field( 'project_user_select',
$value1 . $value2, $post_id );
}

Answer 1

I was able to get this to work using array_merge.
function my_acf_save_post_31( $post_id ) {
// Get new value of field 1
$value1 = get_field( project_manager', $post_id, false );
// Get new value of field 2
$value2 = get_field( 'architect', $post_id, false );
// Get new value of field 3
$value3 = get_field( 'contractor', $post_id, false );
$merge = array_merge($value1,$value2,$value3);
update_field( 'project_user_select', $merge, $post_id );// update
'other_field' with 'my_field' value
}
add_action( 'acf/save_post', 'my_acf_save_post_31', 10 );

Answer 2

If there is a possibility of one of the values being empty I would write it something like this:
// Get new value of field 1 or set value to null
if(!empty(get_field( 'project_manager' )) {
$value1 = get_field( project_manager', $post_id, false );
} else {
$value1 = '';
}
What this does is check if the field has entries, if it does it will assign the value to the variable $value. If the field does not have a value it will just declare the variable so when you try to add each of the $values to $merge it will still work because the variable has been declared.