Query Japanese verbs and their different conjugations

Question

I am pretty new to SPARQL, and I am trying to query Japanese verbs and their different conjugations.

I am not getting any results for the optional ?pastTense, and I can not grasp why.

PREFIX wikibase: <http://wikiba.se/ontology#>
PREFIX dct: <http://purl.org/dc/terms/>
PREFIX wd: <http://www.wikidata.org/entity/>
PREFIX ontolex: <http://www.w3.org/ns/lemon/ontolex#>

SELECT (REPLACE(STR(?lexeme), "http://www.wikidata.org/entity/", "") as ?lexemeID)  ?verb ?pastTense WHERE {
  ?lexeme a ontolex:LexicalEntry ;
    dct:language wd:Q5287 ;
    wikibase:lexicalCategory wd:Q24905 ;
    wikibase:lemma ?verb .
  
  OPTIONAL {
    ?lexeme ontolex:lexicalForm ?pastTenseForm .
    ?pastTenseForm ontolex:representation ?pastTense ;
    wikibase:grammaticalFeature wd:Q106782068 ;               
    }

  BIND(lang(?verb) as ?language)
  FILTER(CONTAINS(?language, "ja-hira") || CONTAINS(?language, "ja"))
  OPTIONAL {
    
  }
}

Answer 1

The issue is with the pattern ?pastTenseForm wikibase:grammaticalFeature wd:Q106782068.

Wikidata doesn’t seem to contain a single statement that has wd:Q106782068 (perfective form) as value for the wikibase:grammaticalFeature property.

It can be shown with this query, which currently has 0 results:

PREFIX wikibase: <http://wikiba.se/ontology#>
PREFIX wd: <http://www.wikidata.org/entity/>

SELECT DISTINCT *

WHERE {
  ?s wikibase:grammaticalFeature wd:Q106782068 .
} LIMIT 1