TMZ broke the story ... Kanye's lawyers filed legal docs claiming prenups in California after 2002 are presumed invalid. It's weird because Kanye himself has NEVER suggested their prenup -- which kept almost all their property separate during their marriage -- is anything other than valid.

As for prenups being presumed invalid ... that's not exactly true. The law says a prenup is presumed invalid IF one of the parties who signed it challenges its validity ... Kanye has not done that, so it's unclear why the lawyers are suggesting it.

What's more ... even if Kanye challenged the prenup, he'd have to show either it was not entered voluntarily or it was "unconscionable." Kanye had a lawyer represent him when the prenup was signed, so it's hard to imagine it wasn't voluntary. As for it being unconscionable, Kanye made a fortune during the marriage and all that money is his ... so this doesn't make sense either.

As for the argument Kanye's lawyers are making -- that his social media posts blasting Pete Davidson and Kim are hearsay -- Kanye himself has never denied posting. In fact, he's said the opposite -- that his account was not hacked. Besides, it's kinda irrelevant whether he posted or not ... Kim simply wants the divorce to become official and then work out custody and any property issues that remain.

Our sources say Kanye has not been working with his lawyers, other than to make his position clear he doesn't want a divorce, but the lawyers haven't really produced any evidence that would carry weight in tomorrow's hearing. And, we're told it's highly unlikely he'll show up for the hearing.