SUP: Location of null type in unions

[philrz]

It's been noted that in SUP output a null in union types is placed last if alongside a primitive type but first if alongside a complex type.

$ super -version &&
  echo 'null' | super -s -c "
    values
      typeof(cast(this, <int64>)),
      typeof(cast(this, <float64>)),
      typeof(cast(this, <bool>)),
      typeof(cast(this, <string>)),
      typeof(cast(this, <bytes>)),
      typeof(cast(this, <ip>)),
      typeof(cast(this, <net>)),
      typeof(cast(this, <time>)),
      typeof(cast(this, <duration>)),
      typeof(cast(this, <[int64]>)),
      typeof(cast(this, <set[int64]>)),
      typeof(cast(this, <map{string:int64}>)),
      typeof(cast(this, <{a:int64}>))
  " -

Version: v0.3.0-123-g0213c531c
<int64|null>
<float64|null>
<bool|null>
<string|null>
<bytes|null>
<ip|null>
<net|null>
<time|null>
<duration|null>
<null|[int64]>
<null|set[int64]>
<null|map{string:int64}>
<null|{a:int64}>

Details

Repro is with super commit 0213c53.

This is effectively a cosmetic issue, but it's been cited as a possible area for UX improvement since being able to spot if a union is nullable may be something users will often want to do. In a brief group discussion there was agreement that it would be nice to standardize here, but there were also some concerns that a change might put the type order in the SUP output out of sync with the underlying type order in BSUP that developers may be familiar with.