#355 document, abstract base, traits and example domain

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasModel.java

@@ -0,0 +1,13 @@
+package com.iluwatar.abstractdocument.domain;
+
+import java.util.Optional;
+
+import com.iluwatar.abstractdocument.Document;
+
+public interface HasModel extends Document {
+	
+	default Optional<String> getModel() {
+		return Optional.ofNullable((String) get("model"));
+	}
+
+}