undef is a state, not a string. Change 'undef' to undef.

ne is a string operator. You can use either == to check if the value is false (which undef is), or better yet, use the defined() function within a for() loop.

This will skip each undefined element, and continue:

for (@MyData){
    next if ! defined;
    ...
}
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This will break out of the loop entirely when it hits the first undef:

for (@MyData){
    last if ! defined;
    ...
}
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