Update Writer\Label.php

Author: jbelien

src/Writer/Label.php

@@ -49,7 +49,7 @@ public function write($label, int $indentSize = 0, string $indent = self::WRITER
             $this->text .= (new Style())->write($label->style, $indentSize + 1, $indent);
         }
 
-        $this->text .= preg_match('/^\(.+\)$/', $label->text) === 1 ? self::getTextRaw('TEXT', $label->text, $indentSize + 1, $indent) : self::getTextString('TEXT', $label->text, $indentSize + 1, $indent);
+        $this->text .= !is_null($label->text) && preg_match('/^\(.+\)$/', $label->text) === 1 ? self::getTextRaw('TEXT', $label->text, $indentSize + 1, $indent) : self::getTextString('TEXT', $label->text, $indentSize + 1, $indent);
         $this->text .= self::getTextRaw('TYPE', $label->type, $indentSize + 1, $indent);
         $this->text .= self::getTextString('WRAP', $label->wrap, $indentSize + 1, $indent);