public TemplateActionDocument addExternalParametersEntry(String key, SsmExternalParameter value) {
        if (null == this.externalParameters) {
            this.externalParameters = new java.util.HashMap<String, SsmExternalParameter>();
        }
        if (this.externalParameters.containsKey(key))
            throw new IllegalArgumentException("Duplicated keys (" + key.toString() + ") are provided.");
        this.externalParameters.put(key, value);
        return this;
    }
Add a single ExternalParameters entry

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