flavorless

Lacking taste or flavor; without seasoning, spice, or discernible qualities of taste.

Salt oysters, on being transferred to fresh water, are "fattened" in the course of two or three days ; if allowed to remain longer they become lean again, and are flavorless.

[…] and as for fruit, the high garden wall was lined with pear trees, spread out flat against it, where they managed to produce a cold, flavorless fruit, a good deal akin to cucumbers.

Flat; lacking character or definition.

1902, Bret Harte, Openings in the Old Trail, IV: A Buckeye Hollow Inheritance, […] and the gravestone of its dead owner on the hill was no more flavorless of his personality than was this plain house in which he had lived and died.

Without flavor.

On the other hand, Pauli had just proposed a massless, chargeless, colorless, flavorless particle whose sole reason for existence was to preserve the principle of momentum conservation.