Added failing test (Thanks to Eliza for reporting the issue)
diff --git a/src/test/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusQueryProcessorTest.java b/src/test/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusQueryProcessorTest.java
index c0b91f7..ee9c52f 100644
--- a/src/test/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusQueryProcessorTest.java
+++ b/src/test/java/de/ids_mannheim/korap/query/serialize/PoliqarpPlusQueryProcessorTest.java
@@ -500,6 +500,11 @@
 
 	@Test
 	public void testLeadingTrailingEmptyTokens() throws JsonProcessingException, IOException {
+		query = "[]";
+		qs.setQuery(query, "poliqarpplus");
+		assertEquals("korap:token",			res.at("/query/@type").asText());
+		assertEquals(true,					res.at("/query/key").isMissingNode());
+
 		query = "[][base=Mann]";
 		qs.setQuery(query, "poliqarpplus");
 		res = mapper.readTree(qs.toJSON());
@@ -1279,4 +1284,4 @@
         
         // TODO more tests
 	}
-}
\ No newline at end of file
+}