[8.x] Fix bug discarding input fields with empty validation rules (#38563)

* Add failing tests

* Fix `ValidationRuleParser` to ignore and preserve empty rules

Author: bakerkretzmar

src/Illuminate/Validation/ValidationRuleParser.php

@@ -292,8 +292,8 @@ public static function filterConditionalRules($rules, array $data = [])
 
             if ($attributeRules instanceof ConditionalRules) {
                 return [$attribute => $attributeRules->passes($data)
-                                ? $attributeRules->rules()
-                                : $attributeRules->defaultRules(), ];
+                                ? array_filter($attributeRules->rules())
+                                : array_filter($attributeRules->defaultRules()), ];
             }
 
             return [$attribute => collect($attributeRules)->map(function ($rule) use ($data) {
@@ -303,6 +303,6 @@ public static function filterConditionalRules($rules, array $data = [])
 
                 return $rule->passes($data) ? $rule->rules() : $rule->defaultRules();
             })->filter()->flatten(1)->values()->all()];
-        })->filter()->all();
+        })->all();
     }
 }

tests/Validation/ValidationRuleParserTest.php

@@ -24,13 +24,29 @@ public function test_conditional_rules_are_properly_expanded_and_filtered()
 
         $this->assertEquals([
             'name' => ['required', 'min:2'],
+            'email' => [],
             'password' => ['required', 'min:2'],
             'username' => ['required', 'min:2'],
             'address' => ['required'],
             'city' => ['required', 'min:2'],
         ], $rules);
     }
 
+    public function test_empty_rules_are_preserved()
+    {
+        $rules = ValidationRuleParser::filterConditionalRules([
+            'name' => [],
+            'email' => '',
+            'password' => Rule::when(true, 'required|min:2'),
+        ]);
+
+        $this->assertEquals([
+            'name' => [],
+            'email' => '',
+            'password' => ['required', 'min:2'],
+        ], $rules);
+    }
+
     public function test_conditional_rules_with_default()
     {
         $rules = ValidationRuleParser::filterConditionalRules([
@@ -49,4 +65,19 @@ public function test_conditional_rules_with_default()
             'address' => ['required', 'string', 'max:10'],
         ], $rules);
     }
+
+    public function test_empty_conditional_rules_are_preserved()
+    {
+        $rules = ValidationRuleParser::filterConditionalRules([
+            'name' => Rule::when(true, '', ['string', 'max:10']),
+            'email' => Rule::when(false, ['required', 'min:2'], []),
+            'password' => Rule::when(false, 'required|min:2', 'string|max:10'),
+        ]);
+
+        $this->assertEquals([
+            'name' => [],
+            'email' => [],
+            'password' => ['string', 'max:10'],
+        ], $rules);
+    }
 }