Why does `@turf/boolean-valid` require `MultiLineString`s to have at least two component `LineString`s?

[benjaminblack]

I assume the OGC Simple Features spec mandates this but I am unable to find a source:

boolean-valid will reject a MultiLineString which has coordinates with only one LineString, e.g. "coordinates": [ [...] ]

The GeoJSON spec is frustratingly silent on whether or not MultiLineString coordinates can be empty; however, we frequently encounter GeoJSON MultiLineStrings composed of a single LineString, typically from GPS devices.

Curiously, for the other multipart geometries, boolean-valid does not enforce this. Why is that?

A GeometryCollection with an empty "geometries": [] is similarly rejected, though the GeoJSON spec explicitly allows this. Again, I assume the reason is the OGC spec, but I can't find a direct source.

As for MultiLineStrings, I observe that the case for MultiLineString is identical to the case for LineString, which would suggest this is a actually a bug; or at least that the MultiLineString case is missing an inner loop to validate that each coordinate has at least lng and lat, as is done with LineStrings.

[sharmaB01]

@benjaminblack just do a change in code here

inlace of case "MultiLineString":
if (coords.length < 2) return false;
put :-
case "MultiLineString":
if (coords.length < 1) return false;

in their file. (https://github.com/Turfjs/turf/blob/master/packages/turf-boolean-valid/index.ts)