According to the crash libgeos/geos#977, the function related to the geometries with EMPTY seems not to be explored by the test suites. Consider this statement:
geos/build/bin/geosop -a 'MULTIPOINT((-2 0), EMPTY)' -b ' GEOMETRYCOLLECTION(POINT(1 0),LINESTRING(0 0,1 0))' distance
# Segmentation fault (core dumped)According to the following definition, ST_Distance returns the minimum distance between two geometries :
returns the minimum 2D Cartesian (planar) distance between two geometries
But the result of ST_Distance(a2, a1) is 3, which is not the minimum distance. Meanwhile, the result of ST_Distance(a2, a1) is not same as ST_Distance( a1, a2). So I believe it is a functional issue that the current test suites haven't explored.