Is the moisture with a urine-like smell in the underwear during sleep, with no trace of wetness, urine or sweat?

If you are not certain about the presence of urine, then doubt is of no consequence, for the default is the purity of garments, and this default is not removed merely by doubt. As the Prophet, peace and blessings be upon him, said to one who doubted the emission of wind during prayer: "He should not leave until he hears a sound or finds a smell." If you find wetness and doubt whether it is urine or sweat, then act upon circumstantial evidence, such as the strong odor of urine which is not mistaken for the smell of sweat; otherwise, the default is the purity of garments.