docs: document the empty state of the no-argument constructor

Close #3

Author: paodb

README.md

@@ -111,6 +111,27 @@ The relative string is computed and updated in the browser by the underlying web
 
 For continuously-ticking elapsed displays use `Format.DURATION` or `Format.MICRO`. `Format.RELATIVE` (the default) collapses past times under a minute to "now". See [SPECIFICATIONS.md](SPECIFICATIONS.md) §2.8 for the full live-update behaviour matrix.
 
+### Components without a value yet
+
+`new RelativeTime()` writes no `datetime` attribute and renders nothing until `setDateTime` is called. No default is applied: the current instant would be a value the caller did not choose, and it would keep ticking away from the intended one until that value arrives.
+
+Use the no-argument constructor when the value is not available at construction time. For an instance-reusing grid renderer:
+
+```java
+grid.addColumn(new ComponentRenderer<>(RelativeTime::new,
+    (rt, task) -> rt.setDateTime(task.getCreated())));
+```
+
+For a display that starts empty and is filled in from a listener:
+
+```java
+RelativeTime preview = new RelativeTime().setFormatStyle(FormatStyle.LONG);
+picker.addValueChangeListener(e -> preview.setDateTime(e.getValue()));
+add(preview);
+```
+
+Call `clear()` to return the component to the empty state.
+
 ## Special configuration when using Spring
 
 By default, Vaadin Flow only includes `com/vaadin/flow/component` to be always scanned for UI components and views. For this reason, the add-on might need to be allowed in order to display correctly. 

SPECIFICATIONS.md

@@ -119,7 +119,8 @@ The cadence depends on the displayed unit:
 ### 3.1 Construction
 
 ```java
-// Empty: datetime can be set later
+// No datetime: renders nothing until setDateTime is called. Intended for component
+// renderers, asynchronously loaded values, and displays that start empty.
 RelativeTime rt = new RelativeTime();
 add(rt);
 
@@ -133,7 +134,7 @@ add(new RelativeTime(LocalDate.of(2025, 1, 1)));
 ```java
 public class RelativeTime extends Component {                 // HasStyle inherited from Component
 
-    public RelativeTime();                                     // empty; datetime can be set later
+    public RelativeTime();                                     // no datetime; renders nothing until set
     public RelativeTime(Instant datetime);
     public RelativeTime(OffsetDateTime datetime);
     public RelativeTime(ZonedDateTime datetime);
@@ -199,7 +200,7 @@ When no configuration is applied:
 - `time-zone` is unset, so absolute-date output uses the viewer's browser default zone.
 - The `title` attribute is set automatically to the absolute formatted date and is surfaced as a native tooltip.
 - The element auto-updates on its own timer; no polling code is needed on the Java side.
-- `RelativeTime` with no `datetime` set renders as an empty inline element.
+- `RelativeTime` with no `datetime` set renders as an empty inline element. No default datetime is applied; see §3.1.
 
 ## 5. Theming
 

src/main/java/com/flowingcode/vaadin/addons/relativetime/RelativeTime.java

@@ -49,6 +49,10 @@
  * the server's. There is no server-side API to read the displayed string; the string lives only
  * in the DOM.
  *
+ * <p><b>Empty state.</b> A component with no target datetime renders nothing: the underlying
+ * element has no text to show. This applies to the {@linkplain #RelativeTime() no-argument
+ * constructor} and to {@link #clear()}. See the constructor for the cases it serves.
+ *
  * <p><b>Attributes, not properties.</b> Setters write HTML attributes
  * ({@code setAttribute}), not DOM properties, because the upstream element is
  * attribute-driven and its kebab-case attribute names match the upstream docs
@@ -94,7 +98,17 @@ public class RelativeTime extends Component {
 
   private Instant lastDateTime;
 
-  /** Creates an empty component. {@link #setDateTime} can be called later. */
+  /**
+   * Creates a relative time component without a target datetime. Renders nothing until
+   * {@link #setDateTime} is called.
+   *
+   * <p>Use this constructor when the datetime is unavailable at creation, such as in component
+   * renderers ({@code new ComponentRenderer<>(RelativeTime::new, ...)}), asynchronous data
+   * loading, or displays reset via {@link #clear()}.
+   *
+   * <p>No default datetime is applied. The current instant would be a value the caller did not
+   * choose, and it would keep ticking away from the intended one until that value arrives.
+   */
   public RelativeTime() {}
 
   /** Creates a component bound to the given instant. */

src/test/java/com/flowingcode/vaadin/addons/relativetime/UseCasesDemo.java

@@ -96,8 +96,10 @@ public UseCasesDemo() {
     addUseCase(layout, "stopwatch",
         "Live stopwatch", buildStopwatch(),
         "A running counter using Format.DURATION (ticks every second from 0s with no \"now\""
-            + " plateau). The Start button pins the datetime to now; Stop clears it. Pattern:"
-            + " timers for in-progress work, build/deploy status, \"uptime since\" indicators.");
+            + " plateau). Built with the no-argument constructor, so it renders nothing until"
+            + " Start pins the datetime to now; Stop clears it and it goes back to empty."
+            + " Pattern: timers for in-progress work, build/deploy status, \"uptime since\""
+            + " indicators.");
 
     addUseCase(layout, "session-expiry",
         "Session expiry warning", buildSessionWarning(),