Fix called and called_with assertions
Fix called and called_with assertions

Need to use `rawget(state, "payload")` instead of `state.payload`
since `state.payload` will never return `nil`. Also use `util.tinsert`
instead of `table.insert` to respect `nil` values.

ZyX-I/luassert,mpeterv/luassert,o-lim/luassert