help with invalid prisma invocation

Invalid `prisma.invite.findMany()` invocation:
Error converting field "groupId" of expected non-nullable type "String", found incompatible value of "null".

model Invite {
    userId  String
    groupId String
    User    User   @relation(fields: [userId], references: [id])
    Group   Group  @relation(fields: [groupId], references: [id])

    @@id([userId, groupId])
}