diff --git a/lib/ACFComposer/ResolveConfig.php b/lib/ACFComposer/ResolveConfig.php
index 24cd26e..c476026 100644
--- a/lib/ACFComposer/ResolveConfig.php
+++ b/lib/ACFComposer/ResolveConfig.php
@@ -10,9 +10,17 @@ public static function forFieldGroup($config) {
 
     $keySuffix = $output['name'];
     $output['key'] = "group_{$keySuffix}";
-    $output['fields'] = array_map(function ($field) use ($keySuffix) {
-      return self::forField($field, [$keySuffix]);
-    }, $output['fields']);
+    $output['fields'] = array_reduce($config['fields'], function ($carry, $fieldConfig) use ($keySuffix) {
+      $fields = self::forField($fieldConfig, [$keySuffix]);
+      if (!self::isAssoc($fields)) {
+        foreach ($fields as $field) {
+          array_push($carry, $field);
+        }
+      } else {
+        array_push($carry, $fields);
+      }
+      return $carry;
+    }, []);
     $output['location'] = array_map('self::mapLocation', $output['location']);
     return $output;
   }
@@ -31,7 +39,13 @@ public static function forLayout($config, $parentKeys = []) {
 
   protected static function forEntity($config, $requiredAttributes, $parentKeys = []) {
     if (is_string($config)) {
-      $config = apply_filters($config, null);
+      $filterName = $config;
+      $config = apply_filters($filterName, null);
+
+      if (is_null($config)) {
+        trigger_error("ACFComposer: Filter {$filterName} does not exist!", E_USER_WARNING);
+        return [];
+      }
     }
     if (!self::isAssoc($config)) {
       return array_map(function ($singleConfig) use ($requiredAttributes, $parentKeys) {
diff --git a/tests/test-resolveConfigForField.php b/tests/test-resolveConfigForField.php
index e17a4be..27c0b1c 100644
--- a/tests/test-resolveConfigForField.php
+++ b/tests/test-resolveConfigForField.php
@@ -71,6 +71,24 @@ function testForFieldGetConfigFromFilter() {
     $this->assertEquals($someField, $output);
   }
 
+  function testForFieldTriggerErrorWithoutFilter() {
+    $config = 'ACFComposer/Fields/someField';
+    Filters::expectApplied($config)
+    ->once()
+    ->andReturn(null);
+    $this->expectException('PHPUnit_Framework_Error_Warning');
+    $output = ResolveConfig::forField($config);
+  }
+
+  function testForFieldReturnEmptyArrayWithoutFilter() {
+    $config = 'ACFComposer/Fields/someField';
+    Filters::expectApplied($config)
+    ->once()
+    ->andReturn(null);
+    $output = @ResolveConfig::forField($config);
+    $this->assertEquals($output, []);
+  }
+
   function testForFieldWithValidSubField() {
     $subFieldConfig = [
       'name' => 'subField',
diff --git a/tests/test-resolveConfigForFieldGroup.php b/tests/test-resolveConfigForFieldGroup.php
index bcd6428..42c4443 100644
--- a/tests/test-resolveConfigForFieldGroup.php
+++ b/tests/test-resolveConfigForFieldGroup.php
@@ -8,11 +8,24 @@
 
 class ResolveConfigForFieldGroupTest extends TestCase {
   function testForFieldGroupWithValidConfig() {
+    $filterName = 'ACFComposer/Fields/someField';
     $fieldConfig = [
       'name' => 'someField',
       'label' => 'Some Field',
       'type' => 'someType'
     ];
+    $fieldConfigMulti = [
+      [
+        'name' => 'someField1',
+        'label' => 'Some Field1',
+        'type' => 'someType'
+      ],
+      [
+        'name' => 'someField2',
+        'label' => 'Some Field2',
+        'type' => 'someType'
+      ]
+    ];
     $locationConfig = [
       'param' => 'someParam',
       'operator' => 'someOperator',
@@ -21,15 +34,26 @@ function testForFieldGroupWithValidConfig() {
     $config = [
       'name' => 'someGroup',
       'title' => 'Some Group',
-      'fields' => [$fieldConfig],
+      'fields' => [
+        $filterName,
+        $fieldConfig,
+        $fieldConfigMulti
+      ],
       'location' => [
         [$locationConfig]
       ]
     ];
+
+    Filters::expectApplied($filterName)
+    ->once()
+    ->andReturn($fieldConfig);
+
     $output = ResolveConfig::forFieldGroup($config);
     $fieldConfig['key'] = 'field_someGroup_someField';
+    $fieldConfigMulti[0]['key'] = 'field_someGroup_someField1';
+    $fieldConfigMulti[1]['key'] = 'field_someGroup_someField2';
     $config['key'] = 'group_someGroup';
-    $config['fields'] = [$fieldConfig];
+    $config['fields'] = [$fieldConfig, $fieldConfig, $fieldConfigMulti[0], $fieldConfigMulti[1]];
     $this->assertEquals($config, $output);
   }