Should we create a null-prototype object?

[theScottyJam]

Should the object returned by groupBy() have a null prototype? It could help add some safety when using the object returned by .groupBy() with unknown keys. Some of the value of this would be lessened if we provide a .groupByMap() function, as being discussed in #3, but it would still be useful either way.

[ljharb]

Not just should, must. This was discussed in plenary; see #1.