field dos not exist within the DocumentSnapshotPlatform

I am trying to build a FutureBuilder but the result of the code gives me Bad state: field dos not exist within the DocumentSnapshotPlatform error.

I searched around before posting this question and found that this error occurs when the "fields" like users and username are not present in firestore but they are clearly present in my firestore. There is a collection named users containing documents with 'uid' as their name. And every doc contains a property username in it.

Following is the code of the `FutureBuilder:

FutureBuilder(
              future: FirebaseFirestore.instance
                  .collection("users")
                  .where(
                    "username",
                    isGreaterThanOrEqualTo: searchController.text,
                  )
                  .get(),
              builder: (context, snapshot) {
                if (!snapshot.hasData) {
                  return const Center(
                    child: CircularProgressIndicator(
                      color: Colors.white,
                    ),
                  );
                }

                return ListView.builder(
                  itemBuilder: (context, index) {
                    return ListTile(
                      leading: CircleAvatar(
                        backgroundImage: NetworkImage(
                          (snapshot.data! as dynamic).docs[index]["photoUrl"],
                        ),
                        radius: 16,
                      ),
                      title: Text(
                        (snapshot.data! as dynamic).docs[index]["username"],
                      ),
                    );
                  },
                  itemCount: (snapshot.data! as dynamic).docs.length,
                );
              },
            ),

Code Explanation: The Appbar contains a TextFormField with a controller searchConroller which will pass the text to future builder in the body section of scaffold. The FutureBuilder will return a ListView which will have ListTile with appropriate username and photoUrl(profile picture) taken from snapshot which we will get from the future.

Why is this error occurring then?