PHP 7.4 Notice: Trying to access array offset on value of type null in inc/acf.php

[richaber]

inc/acf.php makes some assumptions about arrays being present, when they might not actually exist (and are null).

On PHP 7.4, this throws notices like the following:

Notice: Trying to access array offset on value of type null in inc/acf.php on line 24
Notice: Trying to access array offset on value of type null in inc/acf.php on line 53

On Line 24, this can trigger if get_sub_field( 'background_options' ) doesn't return a value, and the ternary tries falling back to get_field( 'background_options' )['background_options']; (where the ['background_options'] array key might be null because get_field did not return an array):

$background_options = get_sub_field( 'background_options' ) ? get_sub_field( 'background_options' ) : get_field( 'background_options' )['background_options'];

Similarly, on Line 53, an assumption is made that we actually have a $background_options['background_type']['value'], which might also be null:

'background_type' => $background_options['background_type']['value'],

In tracing the execution, I can see a lot of null values due to arrays not being present where they were assumed to be, or null array keys...

24: get_sub_field( 'background_options' ) = false
24: get_field( 'background_options' ) = NULL
24: get_field( 'background_options' )['background_options'] = NULL
53: $background_options['background_type']['value'] = NULL