[6.x] Fix Modify::__toString() throwing TypeError for non-string scalar values

src/Modifiers/Modify.php

@@ -90,13 +90,19 @@ public function fetch()
      */
     public function __toString()
     {
-        if (! is_string($this->value) && ! method_exists($this->value, '__toString')) {
-            throw new ModifierException(
-                'Attempted to access modified value as a string, but encountered ['.get_class($this->value).']'
-            );
+        $value = $this->value;
+
+        if ($value === null || is_scalar($value)) {
+            return (string) $value;
+        }
+
+        if (is_object($value) && method_exists($value, '__toString')) {
+            return (string) $value;
         }
 
-        return (string) $this->value;
+        throw new ModifierException(
+            'Attempted to access modified value as a string, but encountered ['.get_debug_type($value).']'
+        );
     }
 
     /**

tests/Modifiers/FluentModifyTest.php

@@ -2,9 +2,11 @@
 
 namespace Tests\Modifiers;
 
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\Attributes\Test;
 use Statamic\Fields\Values;
 use Statamic\Modifiers\Modifier;
+use Statamic\Modifiers\ModifierException;
 use Statamic\Modifiers\Modify;
 use Tests\TestCase;
 
@@ -38,6 +40,42 @@ public function passing_a_values_instance_into_it_will_not_convert_it_to_an_arra
         $this->assertSame($values, $result);
     }
 
+    #[Test]
+    #[DataProvider('scalarValues')]
+    public function it_casts_scalar_and_null_values_to_string($value, $expected)
+    {
+        $this->assertSame($expected, (string) Modify::value($value));
+    }
+
+    public static function scalarValues()
+    {
+        return [
+            'integer zero' => [0, '0'],
+            'positive integer' => [42, '42'],
+            'negative integer' => [-7, '-7'],
+            'float' => [1.5, '1.5'],
+            'true' => [true, '1'],
+            'false' => [false, ''],
+            'null' => [null, ''],
+            'string' => ['hello', 'hello'],
+        ];
+    }
+
+    #[Test]
+    public function it_casts_a_modified_integer_chain_result_to_string()
+    {
+        $this->assertSame('5', (string) Modify::value(0)->add(5));
+    }
+
+    #[Test]
+    public function it_throws_when_casting_an_array_to_string()
+    {
+        $this->expectException(ModifierException::class);
+        $this->expectExceptionMessage('Attempted to access modified value as a string, but encountered [array]');
+
+        (string) Modify::value(['foo' => 'bar']);
+    }
+
     #[Test]
     public function values_instances_get_converted_to_an_array_when_passing_to_a_modifier()
     {