fails:Enumerator::Lazy#flat_map sets nil to size
fails:Enumerator::Lazy#flat_map when the returned lazy enumerator is evaluated by Enumerable#first flattens elements when the given block returned an array or responding to .each and .force
fails:Enumerator::Lazy#flat_map on a nested Lazy sets nil to size
fails:Enumerator::Lazy#flat_map on a nested Lazy when the returned lazy enumerator is evaluated by Enumerable#first flattens elements when the given block returned an array or responding to .each and .force
