First time encountering the phrase “gravitationally lumpy”. I can imagine what that is. But why? I suppose it would naturally occur if the moon were not more or less consistent density. But how would that be possible given the moon’s age and shape. (Roughly spherical I am assuming)
Buried "mascons" (mass concentrations), https://en.wikipedia.org/wiki/Gravitation_of_the_Moon has some nice color maps of the deviations/anomalies. (TLDR: some of it is explained by basalt but not all of it, and it's still being studied, because it interferes with low altitude lunar orbits.)
The moon is also gravitationally very "lumpy", so some small corrections might be needed along the way as well.