Shouldn't duplicate addition to publication be a no-op?

I wonder if trying to add a relation to a publication that it is already a
part should be considered a no-op, instead of causing an error (which
happens in the ALTER PUBLICATION ADD TABLES case).

create table bar (a int);
create publication mypub for table bar;
alter publication mypub add table bar;
ERROR: relation "bar" is already member of publication "mypub"

2nd command should be a no-op, IMHO.

Consider the following (I know we're discussing inheritance elsewhere as
well):

create table foo (a int);
create table baz () inherits (foo);
alter table bar inherit foo;

alter table mypub add table foo;
ERROR: relation "bar" is already member of publication "mypub"

There is no way to add foo and children other than bar to mypub without
doing so one-by-one.

If my proposal to make that a no-op sounds desirable, attached patch
implements that.

Thanks,
Amit