I would like to know it the result of the function "LIST" is correct when a field is empty:
field1 = "A"
field2 = empty
field3 = "B"
I would expect that the returned list has an empty value
This is an expected and often very useful feature of the list function.
Quoting from FileMaker help entry on the list function:
Returns a concatenated list of non-blank values (separated by carriage returns) for a field or fields.