For value of type String?, which statement about value.let and value?.let is correct?

For value of type String?, which statement about value.let and value?.let is correct?

1. value.let always invokes the block with a String?; value?.let skips it for null and supplies a non-null String otherwise.
2. Both forms skip the block when value is null.
3. let rejects nullable receivers at compile time.
4. value?.let invokes the block once with null before returning.