STORE on native array dies when array with holes is passed

[Altai-man]

The Problem

my @foo;
@foo[1] = 5;
my int @bar = @foo;

dies with an uninformative error.

When default is present, it still dies:

my @foo is default(42);
@foo[1] = 5;
my int @bar = @foo;

Expected Behavior

For code to work.

Actual Behavior

Cannot unbox a type object (VMNull) to an int.
  in block <unit> at -e line 1

Steps to Reproduce

➜  ~ perl6 -e 'my @foo; @foo[1] = 42; my int @bar = @foo'
Cannot unbox a type object (VMNull) to an int.
  in block <unit> at -e line 1

Environment

• Operating system: a linux box
• Compiler version (perl6 -v): This is Rakudo version 2019.03 built on MoarVM version 2019.03

[Altai-man]

See https://colabti.org/irclogger/irclogger_log/perl6?date=2019-05-21#l415

[Altai-man]

cast @lizmat
I have overestimated my free time, so don't mind if you take over this issue, according to https://colabti.org/irclogger/irclogger_log/perl6?date=2019-05-21#l443. Good luck.