how to know whether the firestore query is returning anything android code example

Example 1: how to query in firestore

db.collection("cities").where("capital", "==", true)
    .get()
    .then(function(querySnapshot) {
        querySnapshot.forEach(function(doc) {
            // doc.data() is never undefined for query doc snapshots
            console.log(doc.id, " => ", doc.data());
        });
    })
    .catch(function(error) {
        console.log("Error getting documents: ", error);
    });

Example 2: multiple query at once in firebase

function doSomething(...){
    let result1 = [];
    let result2 = [];
    admin.firestore().collection('...').where('some condition').get()
    .then((results: any)=>{
        results.forEach((element: any)=>{
            if(some other condition){
                result1.push(element);
            }
    })
    .catch((error: any)=>{//log the error});
    admin.firestore().collection('...').where('yet another condition').orderBy(...).get()
    .then((results: any)=>{
        results.forEach((element: any)=>{
            result2.push(func(element))  //func is some manipulation
    })
    .catch((error: any)=>{//log the error});
    return makeCalculation(result1, result2);
}