only forward non nullish mapped data

lib/query.js

@@ -164,7 +164,15 @@ module.exports = class Query extends Readable {
       this._slowdown = false
     }
 
-    if (m.status !== 0 || this.push(this.map(m)) !== false) this._readMore()
+    if (m.status !== 0) {
+      this._readMore()
+      return
+    }
+
+    const data = this.map(m)
+    if (!data || this.push(data) !== false) {
+      this._readMore()
+    }
   }
 
   _onerror () {