Remove empty string for routes_lines layer - vtiles

Author: Rub21

images/tiler-server/config/providers/route_lines.toml

@@ -7,20 +7,20 @@ sql = """
 SELECT 
     ST_AsMVTGeom(geometry, !BBOX!) AS geometry,
     ABS(osm_id) AS osm_id,
-    name,
-    type,
-    route,
-    ref,
-    network,
-    direction,
-    operator,
-    state,
-    symbol,
+    NULLIF(name, '') AS name,
+    NULLIF(type, '') AS type,
+    NULLIF(route, '') AS route,
+    NULLIF(ref, '') AS ref,
+    NULLIF(network, '') AS network,
+    NULLIF(direction, '') AS direction,
+    NULLIF(operator, '') AS operator,
+    NULLIF(state, '') AS state,
+    NULLIF(symbol, '') AS symbol,
     distance,
-    roundtrip,
-    interval,
-    duration,
-    tourism,
+    NULLIF(roundtrip, '') AS roundtrip,
+    NULLIF(interval, '') AS interval,
+    NULLIF(duration, '') AS duration,
+    NULLIF(tourism, '') AS tourism,
     NULLIF(start_date, '') AS start_date, 
     NULLIF(end_date, '') AS end_date, 
     isodatetodecimaldate(pad_date(start_date, 'start'), FALSE) AS start_decdate,