Fix bug: can handle empty text nodes in Xournal++

src/xopp2oml/template.oml

@@ -43,7 +43,7 @@ description <{{output_namespace}}#> as {{shorthand}} {
   ]
 
   {%- for el_index, el in enumerate(layer.elements) %}
-  {%- if not minimal or el.__class__.__name__ == "Text" %}
+  {%- if not minimal or el.__class__.__name__ == "Text" and el.text != None %}
 
   ci p{{page_index}}l{{layer_index}}e{{el_index}} : xopp:{{el.__class__.__name__}} [
     xopp:hasText {{el.text | to_oml_string_literal}}