This paper investigates the knowledge of constructions with absent expletives by advanced and high-proficiency non-native speakers of German whose first language is Polish. German grammar is known to license null subjects due to the strength of AGRP but not to identify them. Therefore only expletive subjects can be absent in German, except for Topic-drop and, crucially, the expletive subjects have to be absent in certain cases due to the Projection Principle. The knowledge of this phenomenon by second language (L2) learners has been investigated by two methods, elicited written production task and grammaticality judgment tests. High-level non-native speakers of German differ significantly from native speakers in both types of tasks. The differences are clearly not the result of transfer. The results reported here reveal permanent optionality in L2 grammars suggesting a deficit in the grammatical representations of L2 learners.