Nothing seems wrong with your code, here is the full version:
CouchDbClient dbClient = new CouchDbClient();
DesignDocument designDocument = new DesignDocument();
designDocument.setId("_design/mydesign");
designDocument.setLanguage("javascript");
MapReduce get_numberOfSeasonsMR = new MapReduce();
get_numberOfSeasonsMR.setMap(
"function(doc) { "
+ " emit(doc.seriesName, doc.season)"
+ "}");
get_numberOfSeasonsMR.setReduce(
"function (key, values, rereduce) {"
+ "return Math.max.apply({}, values)"
+ "}");
Map<String, MapReduce> view = new HashMap<>();
view.put("get_numberOfSeasons", get_numberOfSeasonsMR);
designDocument.setViews(view);
dbClient.design().synchronizeWithDb(designDocument);
int count = dbClient.view("mydesign/get_numberOfSeasons").key("Arrow").queryForInt();