Autovifivication means that

EXPR1->[ EXPR2 ]
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is short for

( EXPR1 //= [] )->[ EXPR2 ]
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This makes sense:

$list //= []
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This doesn't make sense:

get_no_list() //= []
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You can't assign to a non-lvalue function.

If you want the first element of a list, you can use a list slice.

( some_list() )[0]  # Returns the first element or an empty list.
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