add_test: empty argument regression in 3.27.0-rc1

With this example:

cmake_minimum_required(VERSION 3.26)
project(Foo NONE)
enable_testing()
add_test(NAME foo COMMAND /usr/bin/echo "a" "" "b")

Using CMake 3.26.4:

$ ctest -N -V | grep echo
1: Test command: /usr/bin/echo "a" "" "b"

Using CMake 3.27.0-rc1:

$ ctest -N -V | grep echo
1: Test command: /usr/bin/echo "a" "b"

Note that the empty argument was dropped.