It says in the Pasuk in Bamidbar ‘In a dream shall I speak to him (the navi)’
But it also says in Zecharyah 10: ‘And dreams, they speak in vain’
I view it this way: When Hashem speaks to a true navi, it is in dreams. If anyone else (nowadays)who would not be worthy of such, claims nevuah in a dream, the dream was in vain.