Fix major bug in Property::clear

Author: thiemowmde

src/Entity/Property.php

@@ -237,6 +237,7 @@ public function isEmpty() {
 	 */
 	public function clear() {
 		$this->fingerprint = new Fingerprint();
+		$this->statements = new StatementList();
 	}
 
 	/**

tests/unit/Entity/PropertyTest.php

@@ -118,14 +118,14 @@ public function testPropertyWithFingerprintIsNotEmpty() {
 
 	public function testClearRemovesAllButId() {
 		$property = Property::newFromType( 'string' );
-
 		$property->setId( 42 );
 		$property->getFingerprint()->setLabel( 'en', 'foo' );
+		$property->getStatements()->addNewStatement( new PropertyNoValueSnak( 1 ) );
 
 		$property->clear();
 
 		$this->assertEquals( new PropertyId( 'P42' ), $property->getId() );
-		$this->assertTrue( $property->getFingerprint()->isEmpty() );
+		$this->assertTrue( $property->isEmpty() );
 	}
 
 	public function testGetStatementsReturnsEmptyListForEmptyProperty() {