Previously the appendChild / removeChild could take null as an argument for
a child to be added / removed. This is difficult to understand since the
mentioned methods are noop if a child is null.
This commit clarifies the appendChild / removeChild signature to systematically
require a child node to be added removed. It turns out that null could be passed
only for a very specific i18n cases so now we guard a call to removeChild with
an explicit check on the i18n side.
PR Close#27987
b432eb1cae