code: public NumberExpression<Double> distance(Expression<? extends Geometry> geometry) {
          return Expressions.numberOperation(Double.class, SpatialOps.DISTANCE, mixin, geometry);
      }
docs: Returns the shortest distance between any two Points in the two geometric objects as
  calculated in the spatial reference system of this geometric object. Because the geometries
  are closed, it is possible to find a point on each geometric object involved, such that the
  distance between these 2 points is the returned distance between their geometric objects.
  
  @param geometry other geometry
  @return distance between this and the other geometry