#355 override toString to log properties

abstract-document/src/main/java/com/iluwatar/abstractdocument/AbstractDocument.java

@@ -31,8 +31,19 @@ public abstract class AbstractDocument implements Document {
         return Stream.of(get(key))
                 .filter(el -> el != null)
                 .map(el -> (List<Map<String, Object>>) el)
-				.findFirst().get().stream()
+                .findAny().get().stream()
                 .map(constructor);
     }
 
+    @Override
+    public String toString() {
+        final StringBuilder builder = new StringBuilder();
+        builder.append(getClass().getName()).append("[");
+        properties.entrySet().forEach(e ->
+                builder.append("[").append(e.getKey()).append(" : ").append(e.getValue()).append("]")
+        );
+        builder.append("]");
+        return builder.toString();
+    }
+
 }