The Following Works Correctly for me and the following info is

1- @JsonFormat check over each element of the Collection to be in the format dd-MM-yyyy

2- added @Future to check that sent date into the future


    @JsonFormat(shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy") // to ensure that the date format sent in dd-MM-yyyy
    private Set<@NotNull(message = "Each date in Session Scheduler must not be null")
                @Future(message = "Each Session Scheduler Date must be In Future") LocalDate> sessionScheduler;