public ReferenceSets addIPSetReferencesEntry(String key, IPSetReference value) {
        if (null == this.iPSetReferences) {
            this.iPSetReferences = new java.util.HashMap<String, IPSetReference>();
        }
        if (this.iPSetReferences.containsKey(key))
            throw new IllegalArgumentException("Duplicated keys (" + key.toString() + ") are provided.");
        this.iPSetReferences.put(key, value);
        return this;
    }
Add a single IPSetReferences entry

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