ST_SnapToGrid returns non-typed empties

[strk]

strk=# select ST_AsEWKT(ST_SnapToGrid('MULTIPOLYGON(((0 0, 10 0, 10 10, 0 10, 0 0)))'::geometry, 20));
        st_asewkt         
--------------------------
 GEOMETRYCOLLECTION EMPTY
(1 row)

Compare with ST_Simplify, which supports empties:

strk=# select ST_AsEWKT(ST_Simplify('POLYGON((0 0, 10 0, 10 10, 0 10, 0 0))'::geometry, 20));
   st_asewkt   
---------------
 POLYGON EMPTY
(1 row)

[strk]

Fixed in r9516