public String getUserId() {
        return this.userId;
    }
<p>
The ID of an Amazon Web Services account.
</p>
<p>
For a referenced security group in another VPC, the account ID of the referenced security group is returned in
the response. If the referenced security group is deleted, this value is not returned.
</p>
<p>
[EC2-Classic] Required when adding or removing rules that reference a security group in another VPC.
</p>

@return The ID of an Amazon Web Services account.</p>
        <p>
        For a referenced security group in another VPC, the account ID of the referenced security group is
        returned in the response. If the referenced security group is deleted, this value is not returned.
        </p>
        <p>
        [EC2-Classic] Required when adding or removing rules that reference a security group in another VPC.
aws-java-sdk-securityhub/src/main/java/com/amazonaws/services/securityhub/model/AwsEc2SecurityGroupUserIdGroupPair.java