[perl #123216] [BUG] QRPA: Can't pop from an empty array!

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# New Ticket Created by  V V 
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Not sure what is causing this (using Perl only a few days). I have the
following example

    use v6 ;
    sub infix:«MYPLUS»(*@a) is assoc('list') {
        [+] @a ;
    }

    sub prefix:«MYMINUS»($a) is looser(&infix:<MYPLUS>) {
        -$a ;
    }

    # QRPA: Can't pop from an empty array!
    say (MYMINUS 1 MYPLUS 2 MYPLUS 3) ;

However the following equivalent example works as expected

    use v6 ;
    sub prefix:«MYMINUS»($a) {
        -$a ;
    }

    sub infix:«MYPLUS»(*@a) is assoc('list') is tighter(&prefix:<MYMINUS>) {
        [+] @a ;
    }

    # prints -6 as expected
    say (MYMINUS 1 MYPLUS 2 MYPLUS 3) ;

Output of perl6 --version is
This is perl6 version 2014.10-121-g7dd7292 built on parrot 6.9.0
revision RELEASE_6_9_0-72-g4b90157

Thanks,
Vladimir