diff --git a/src/Micrometa/Application/Item/PropertyList.php b/src/Micrometa/Application/Item/PropertyList.php
index acb7fdc..addc173 100755
--- a/src/Micrometa/Application/Item/PropertyList.php
+++ b/src/Micrometa/Application/Item/PropertyList.php
@@ -77,7 +77,7 @@ public function __construct(AliasFactoryInterface $aliasFactory)
      * @param \stdClass|string $iri IRI
      * @param array $value          Property values
      */
-    public function offsetSet($iri, $value)
+    public function offsetSet($iri, $value): void
     {
         $iri                    = IriFactory::create($iri);
         $iriStr                 = strval($iri);
@@ -124,7 +124,7 @@ function (ExportableInterface $value) {
      *
      * @return int Property cursor
      */
-    protected function getPropertyCursor($name)
+    protected function getPropertyCursor($name): int
     {
         // Run through all property names
         foreach ($this->names as $cursor => $iri) {
diff --git a/src/Micrometa/Domain/Item/Item.php b/src/Micrometa/Domain/Item/Item.php
index 97949c7..b2b5b04 100755
--- a/src/Micrometa/Domain/Item/Item.php
+++ b/src/Micrometa/Domain/Item/Item.php
@@ -73,8 +73,8 @@ public function __construct(
             $propertyListFactory ?: new PropertyListFactory(),
             is_array($type) ? $type : [$type],
             $properties,
-            trim($itemId),
-            trim($itemLanguage)
+            $itemId ? trim($itemId) : null,
+            $itemLanguage ? trim($itemLanguage) : null
         );
     }
 
diff --git a/src/Micrometa/Domain/Item/PropertyList.php b/src/Micrometa/Domain/Item/PropertyList.php
index cf9b591..71fd6de 100755
--- a/src/Micrometa/Domain/Item/PropertyList.php
+++ b/src/Micrometa/Domain/Item/PropertyList.php
@@ -80,7 +80,7 @@ class PropertyList implements PropertyListInterface
      *
      * @throws ErrorException
      */
-    public function offsetUnset($iri)
+    public function offsetUnset($iri): void
     {
         throw new ErrorException(
             sprintf(ErrorException::CANNOT_UNSET_PROPERTY_STR, $iri),
@@ -94,7 +94,7 @@ public function offsetUnset($iri)
      *
      * @return int Number of properties
      */
-    public function count()
+    public function count(): int
     {
         return count($this->values);
     }
@@ -104,7 +104,7 @@ public function count()
      *
      * @return array Property values
      */
-    public function current()
+    public function current(): array
     {
         return $this->values[$this->cursor];
     }
@@ -112,7 +112,7 @@ public function current()
     /**
      * Move forward to next element
      */
-    public function next()
+    public function next(): void
     {
         ++$this->cursor;
     }
@@ -120,7 +120,7 @@ public function next()
     /**
      * Return the current IRI key
      *
-     * @return \stdClass IRI key
+     * @return mixed IRI key
      */
     public function key()
     {
@@ -132,7 +132,7 @@ public function key()
      *
      * @return boolean The current position is valid
      */
-    public function valid()
+    public function valid(): bool
     {
         return isset($this->values[$this->cursor]);
     }
@@ -140,7 +140,7 @@ public function valid()
     /**
      * Rewind the Iterator to the first element
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->cursor = 0;
     }
@@ -173,7 +173,7 @@ public function add($property)
      *
      * @return boolean Property exists
      */
-    public function offsetExists($iri)
+    public function offsetExists($iri): bool
     {
         $iri = IriFactory::create($iri);
         try {
@@ -246,7 +246,7 @@ protected function getPropertyCursor($name)
      * @param \stdClass|Iri|string $iri IRI
      * @param array $value              Property values
      */
-    public function offsetSet($iri, $value)
+    public function offsetSet($iri, $value): void
     {
         $iri                   = IriFactory::create($iri);
         $iriStr                = strval($iri);
@@ -264,7 +264,7 @@ public function offsetSet($iri, $value)
      * @return array Property values
      * @throws OutOfBoundsException If the property name is unknown
      */
-    public function &offsetGet($iri)
+    public function &offsetGet($iri): array
     {
         $iri    = IriFactory::create($iri);
         $cursor = ($iri->profile !== '') ?
diff --git a/src/Micrometa/Domain/Item/PropertyListInterface.php b/src/Micrometa/Domain/Item/PropertyListInterface.php
index 43091a2..348e8a5 100755
--- a/src/Micrometa/Domain/Item/PropertyListInterface.php
+++ b/src/Micrometa/Domain/Item/PropertyListInterface.php
@@ -51,7 +51,7 @@ interface PropertyListInterface extends \ArrayAccess, \Iterator, \Countable
      *
      * @return boolean Property exists
      */
-    public function offsetExists($iri);
+    public function offsetExists($iri): bool;
 
     /**
      * Get a particular property
@@ -60,7 +60,7 @@ public function offsetExists($iri);
      *
      * @return array Property values
      */
-    public function &offsetGet($iri);
+    public function &offsetGet($iri): array;
 
     /**
      * Set a particular property
@@ -68,14 +68,14 @@ public function &offsetGet($iri);
      * @param \stdClass|string $iri IRI
      * @param array $value          Property values
      */
-    public function offsetSet($iri, $value);
+    public function offsetSet($iri, $value): void;
 
     /**
      * Unset a property
      *
      * @param \stdClass|string $iri IRI
      */
-    public function offsetUnset($iri);
+    public function offsetUnset($iri): void;
 
     /**
      * Add a property
diff --git a/src/Micrometa/Ports/Item/Item.php b/src/Micrometa/Ports/Item/Item.php
index 89ee4fb..1e584f5 100755
--- a/src/Micrometa/Ports/Item/Item.php
+++ b/src/Micrometa/Ports/Item/Item.php
@@ -363,7 +363,7 @@ public function getFirstItem(...$types)
      *
      * @return int
      */
-    public function count()
+    public function count(): int
     {
         return $this->itemList->count();
     }
diff --git a/src/Micrometa/Ports/Item/ItemList.php b/src/Micrometa/Ports/Item/ItemList.php
index 5acfbfb..d42c889 100755
--- a/src/Micrometa/Ports/Item/ItemList.php
+++ b/src/Micrometa/Ports/Item/ItemList.php
@@ -91,7 +91,7 @@ public function current()
      * @return void
      * @api
      */
-    public function next()
+    public function next(): void
     {
         ++$this->pointer;
     }
@@ -102,7 +102,7 @@ public function next()
      * @return int Position of the current element
      * @api
      */
-    public function key()
+    public function key(): int
     {
         return $this->pointer;
     }
@@ -113,7 +113,7 @@ public function key()
      * @return boolean The current position is valid
      * @api
      */
-    public function valid()
+    public function valid(): bool
     {
         return isset($this->items[$this->pointer]);
     }
@@ -124,7 +124,7 @@ public function valid()
      * @return void
      * @api
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->pointer = 0;
     }
@@ -137,7 +137,7 @@ public function rewind()
      * @return boolean Offset exists
      * @api
      */
-    public function offsetExists($offset)
+    public function offsetExists($offset): bool
     {
         return isset($this->items[$offset]);
     }
@@ -164,7 +164,7 @@ public function offsetGet($offset)
      *
      * @api
      */
-    public function offsetSet($offset, $value)
+    public function offsetSet($offset, $value): void
     {
         throw new RuntimeException(RuntimeException::IMMUTABLE_ITEM_LIST_STR, RuntimeException::IMMUTABLE_ITEM_LIST);
     }
@@ -175,7 +175,7 @@ public function offsetSet($offset, $value)
      * @param int $offset Offset
      * @SuppressWarnings(PHPMD.UnusedFormalParameter)
      */
-    public function offsetUnset($offset)
+    public function offsetUnset($offset): void
     {
         throw new RuntimeException(RuntimeException::IMMUTABLE_ITEM_LIST_STR, RuntimeException::IMMUTABLE_ITEM_LIST);
     }
@@ -250,7 +250,7 @@ function (ItemInterface $item) use ($types) {
      * @return int Number of items
      * @api
      */
-    public function count()
+    public function count(): int
     {
         return count($this->items);
     }