Fix an issue where not having a default empty choice (even with an em…

…pty label) would cause selectize to select the first option instead of displaying the placeholder

src/Charcoal/Admin/Property/Input/SelectizeInput.php

@@ -201,6 +201,19 @@ protected function collectionLoader()
         return $this->collectionLoader;
     }
 
+    /**
+     * Retrieve the default empty option structure.
+     *
+     * @return array
+     */
+    protected function defaultEmptyChoice()
+    {
+        return [
+            'value' => '',
+            'label' => ''
+        ];
+    }
+
     /**
      * Retrieve the selectable options.
      *
@@ -211,6 +224,11 @@ protected function collectionLoader()
      */
     public function choices()
     {
+        if ($this->p()->allowNull() && !$this->p()->multiple()) {
+            $prepend = $this->parseChoice('', $this->emptyChoice());
+            yield $prepend;
+        }
+
         // When deferred, we want to fetch choices for current values only.
         if ($this->deferred()) {
             $choices = $this->selectizeVal($this->propertyVal());