Set the default type to select.

It is the implicit default anyways. If a query object does not have
another query type method called it should behave like a select query.
This change removes annoying failures when using mocked queries.

Cake/Database/Query.php

@@ -47,7 +47,7 @@ class Query implements ExpressionInterface, IteratorAggregate {
  *
  * @var string
  */
-	protected $_type;
+	protected $_type = 'select';
 
 /**
  * List of SQL parts that will be used to build this query

Cake/ORM/Query.php

@@ -417,7 +417,7 @@ public function setResult($results) {
  *   queries a statement will be returned.
  */
 	public function execute() {
-		if ($this->_type === 'select' || $this->_type === null) {
+		if ($this->_type === 'select') {
 			$table = $this->repository();
 			$event = new Event('Model.beforeFind', $table, [$this, $this->_options]);
 			$table->getEventManager()->dispatch($event);