If 'a' is a name or description that does not refer, then Fa is false and ~(Fa) is true.

In the empty domain, all values of x do not refer.

Therefore..

ExFx is false in the empty domain, and Ex~(Fx) is true.

ie. Fa v Fb v Fc ... is false, and ~(Fa) v ~(Fb) v ~(Fc)...is true.

Therefore..

AxFx is false in the empty domain, and Ax~(Fx) is true.

ie. Fa & Fb & Fc ... is false, and ~(Fa) & ~(Fb) & ~(Fc) ..is true.

That is, (AxFx -> ExFx) is true in the empty domain