public SendUsersMessageRequest addUsersEntry(String key, EndpointSendConfiguration value) {
        if (null == this.users) {
            this.users = new java.util.HashMap<String, EndpointSendConfiguration>();
        }
        if (this.users.containsKey(key))
            throw new IllegalArgumentException("Duplicated keys (" + key.toString() + ") are provided.");
        this.users.put(key, value);
        return this;
    }
Add a single Users entry

@see SendUsersMessageRequest#withUsers
@returns a reference to this object so that method calls can be chained together.
aws-java-sdk-pinpoint/src/main/java/com/amazonaws/services/pinpoint/model/SendUsersMessageRequest.java