Issue #2862673 by masipila, Pavan B S, Jo Fitzgerald, phenaproxima: Add...

Issue #2862673 by masipila, Pavan B S, Jo Fitzgerald, phenaproxima: Add documentation to EmptySource source plugin

core/modules/migrate/src/Plugin/migrate/source/EmptySource.php

@@ -3,9 +3,20 @@
 namespace Drupal\migrate\Plugin\migrate\source;
 
 /**
- * Source returning an empty row.
+ * Source returning a row based on the constants provided.
  *
- * This is generally useful when needing to create a field using a migration..
+ * Example:
+ *
+ * @code
+ * source:
+ *   plugin: empty
+ *   constants:
+ *     entity_type: user
+ *     field_name: image
+ * @endcode
+ *
+ * This will return a single row containing 'entity_type' and 'field_name'
+ * elements, with values of 'user' and 'image', respectively.
  *
  * @MigrateSource(
  *   id = "empty"