Of course, most of the sutras in the third turning of the wheel say the tathāgatagarbha is not empty, but there is no contradiction here. The essence of tathāgatagarbha, like all other phenomena, is empty, but the luminous, clear light aspect of tathāgatagarbha is not empty. This luminosity or clear light from which impure and pure appearances manifest is permanent and everlasting. The followers at this time had already established a foundation in the second turning of the wheel, so even if the Buddha used words like not empty, permanent, and everlasting to describe the tathāgatagarbha, they would not develop an attachment to clear light. It was perfectly clear to everyone—all phenomena, whether in samsara or nirvana, are completely empty of true existence.
~Depicted from GATEWAY TO VAJRAYANA PATH - Vajrayana Terminology