get() {
            return when (this) {
                is ConeErrorType -> when (val diagnostic = this.diagnostic) {
                    // Tolerate code that misses type parameters while shortening it.
                    is ConeUnmatchedTypeArgumentsError -> diagnostic.symbol.classId
                    else -> null
                }
                is ConeClassLikeType -> lookupTag.classId

                // implicit invoke call. For example,
                // ```
                // fun test(f: () -> Unit) {
                //   f() // calleeExpression `f` resolves to the local variable access, while `f()` resolves to the implicit `invoke` call.
                //       // This way `f` is also the explicit receiver of this implicit `invoke` call
                // }
                // ```