diff --git a/src/Concept.php b/src/Concept.php
index 6144e72..824eb10 100644
--- a/src/Concept.php
+++ b/src/Concept.php
@@ -16,14 +16,14 @@ class Concept extends Item
     ];
 
     const FIELDS = [
-        'narrower'      => ['Set','Concept'],
-        'broader'       => ['Set','Concept'],
-        'related'       => ['Set','Concept'],
-        'previous'      => ['Set','Concept'],
-        'next'          => ['Set','Concept'],
-        'ancestors'     => ['Set','Concept'],
-        'inScheme'      => ['Set','ConceptScheme'],
-        'topConceptOf'  => ['Set','ConceptScheme'],
+        'narrower'      => ['Set', 'Concept'],
+        'broader'       => ['Set', 'Concept'],
+        'related'       => ['Set', 'Concept'],
+        'previous'      => ['Set', 'Concept'],
+        'next'          => ['Set', 'Concept'],
+        'ancestors'     => ['Set', 'Concept'],
+        'inScheme'      => ['Set', 'ConceptScheme'],
+        'topConceptOf'  => ['Set', 'ConceptScheme'],
     ];
 
     /**
diff --git a/src/Container.php b/src/Container.php
index 14520be..39eda88 100644
--- a/src/Container.php
+++ b/src/Container.php
@@ -169,7 +169,7 @@ public function getIterator()
 
     public function jsonLDSerialize(string $context = self::DEFAULT_CONTEXT, bool $types = null)
     {
-        $set = array_map(function ($m) use ($types) {
+        $set = array_map(function($m) use ($types) {
             return is_object($m) ? $m->jsonLDSerialize('', $types) : $m;
         }, $this->members);
 
diff --git a/src/DataType.php b/src/DataType.php
index a2170a6..733479e 100644
--- a/src/DataType.php
+++ b/src/DataType.php
@@ -48,7 +48,7 @@ protected static function fieldType(string $field, bool $strict = false)
         }
     }
 
-    private function fieldException($field, $message)
+    private function fieldException(string $field, string $message)
     {
         return new InvalidArgumentException(
             get_called_class() . "->$field must $message"
@@ -74,7 +74,7 @@ protected function setField(string $field, $value, bool $strict = true)
                     if (is_array($value)) {
                         $class = 'JSKOS\\' . $type[1];
                         $value = new Set(
-                            array_map(function ($m) use ($class) {
+                            array_map(function($m) use ($class) {
                                 if (is_null($m)) {
                                     return null;
                                 }
@@ -99,8 +99,6 @@ protected function setField(string $field, $value, bool $strict = true)
                 }
                 # TODO: check member types
             }
-        } elseif ($type == '*') {
-            $value = $value;
         } elseif ($type == 'LanguageMapOfStrings') {
             if (!($value instanceof LanguageMapOfStrings)) {
                 $value = new LanguageMapOfStrings($value);
@@ -109,12 +107,12 @@ protected function setField(string $field, $value, bool $strict = true)
             if (!($value instanceof LanguageMapOfLists)) {
                 $value = new LanguageMapOfLists($value);
             }
-        } elseif (!DataType::hasType($value, $type)) {
-            if ($type == 'ConceptScheme') {
+        } elseif ($type == 'ConceptScheme') {
+            if (!($value instanceof ConceptScheme)) {
                 $value = new ConceptScheme($value);
-            } else {
-                throw $this->fieldException($field, "match JSKOS\DataType::is$type");
             }
+        } elseif ($type != '*' && !DataType::hasType($value, $type)) {
+            throw $this->fieldException($field, "match JSKOS\DataType::is$type");
         }
 
         $this->$field = $value;
diff --git a/src/Resource.php b/src/Resource.php
index fc99c2f..ce7204d 100644
--- a/src/Resource.php
+++ b/src/Resource.php
@@ -26,10 +26,10 @@ abstract class Resource extends DataType
         'created'     => 'Date',
         'issued'      => 'Date',
         'modified'    => 'Date',
-        'creator'     => ['Set','Concept'],
-        'contributor' => ['Set','Concept'],
-        'publisher'   => ['Set','Concept'],
-        'partOf'      => ['Set','Concept'],
+        'creator'     => ['Set', 'Concept'],
+        'contributor' => ['Set', 'Concept'],
+        'publisher'   => ['Set', 'Concept'],
+        'partOf'      => ['Set', 'Concept'],
     ];
 
     /**
diff --git a/tests/LanguageMapOfStringsTest.php b/tests/LanguageMapOfStringsTest.php
index e65934e..10b0eb7 100644
--- a/tests/LanguageMapOfStringsTest.php
+++ b/tests/LanguageMapOfStringsTest.php
@@ -19,6 +19,9 @@ public function testConstruct()
 
         $nonstrict = new LanguageMapOfStrings([0=>[], 'en'=>'hi']);
         $this->assertEquals($map, $nonstrict);
+
+        $map['en'] = null;
+        $this->assertEquals(new LanguageMapOfStrings(), $map);
     }
 
     public function testJson()
diff --git a/tests/SetTest.php b/tests/SetTest.php
index 6c0ca98..011a52e 100644
--- a/tests/SetTest.php
+++ b/tests/SetTest.php
@@ -7,6 +7,7 @@
 
 /**
  * @covers JSKOS\Set
+ * @covers JSKOS\Container
  */
 class SetTest extends \PHPUnit\Framework\TestCase
 {