I`m currently making a set of custom OCLint rules for my university and I need to catch statements like:

char *str = strdup("Hello, world!");
if (str == NULL) {   // That`s what i`m interested in
    ...
}

So how do I check if an Expr is NULL? I know there is a method Expr::isNullPointerConstant(ASTContext &Ctx, NullPointerConstantValueDependence NPC), but I don’t know how to get ASTContext from my oclint::AbstractASTVisitorRule. There are no mentions of anything like that in documentation (or that`s just me, idk _(0_0)_/)

How do I do that?