Fix bug where calling 'context.with((ImplicitContextKeyed) null)' drops all other elements. (#11672)

Fix bug where calling 'context.with((ImplicitContextKeyed) null)' drops all other elements.

Co-authored-by: devflow.devflow-routing-intake <devflow.devflow-routing-intake@kubernetes.us1.ddbuild.io>

Author: mcculls

components/context/src/main/java/datadog/context/Context.java

@@ -155,7 +155,7 @@ default <T, U> Context with(
    */
   default Context with(@Nullable ImplicitContextKeyed value) {
     if (value == null) {
-      return root();
+      return this;
     }
     return value.storeInto(this);
   }

components/context/src/test/java/datadog/context/ContextTest.java

@@ -60,8 +60,10 @@ void testWith(Context context) {
     // Test null value handling
     assertDoesNotThrow(
         () -> context.with(BOOLEAN_KEY, null), "Null value should not throw exception");
-    // Test null implicitly keyed value handling
-    assertDoesNotThrow(() -> context.with(null), "Null implicitly keyed value not throw exception");
+    // Test null implicitly keyed value handling - should preserve existing context, not discard it
+    Context withNull = context1.with((ImplicitContextKeyed) null);
+    assertEquals(
+        context1, withNull, "Null implicitly keyed value should preserve existing context");
   }
 
   @ParameterizedTest