Don't allow creating empty list of references

Author: stloyd

src/core/etl/src/Flow/ETL/Row/References.php

@@ -24,6 +24,10 @@ final class References implements \ArrayAccess, \Countable, \IteratorAggregate
 
     public function __construct(string|Reference ...$references)
     {
+        if ([] === $references) {
+            throw new InvalidArgumentException('References cannot be empty.');
+        }
+
         foreach ($references as $ref) {
             $ref = EntryReference::init($ref);
 

src/core/etl/tests/Flow/ETL/Tests/Unit/Row/ReferencesTest.php

@@ -5,14 +5,23 @@
 namespace Flow\ETL\Tests\Unit\Row;
 
 use function Flow\ETL\DSL\{ref, refs};
+use Flow\ETL\Exception\InvalidArgumentException;
 use Flow\ETL\Row\References;
 use Flow\ETL\Tests\FlowTestCase;
 
 final class ReferencesTest extends FlowTestCase
 {
+    public function test_empty() : void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('References cannot be empty.');
+
+        refs();
+    }
+
     public function test_lazy_without() : void
     {
-        $refs = refs()->without('id')->add('id')->add('name');
+        $refs = refs('id')->without('id')->add('id')->add('name');
 
         self::assertEquals(
             refs('name')->all(),