Android : com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String

Question

private void fetchData(DataSnapshot dataSnapshot)
{
    spacecrafts.clear();

    for (DataSnapshot ds : dataSnapshot.getChildren())
    {
        Spacecraft spacecraft=ds.getValue(Spacecraft.class);
        spacecrafts.add(spacecraft);
    }
}

Spacecraft spacecraft=ds.getValue(Spacecraft.class); This line returns below error

com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type lk.magesty.covidnewssrilanka.m_Model.Spacecraft

Anyone know a solution for this ?

Spacecraft.java file

package lk.magesty.covidnewssrilanka.m_Model;

public class Spacecraft {
    String name,propellant,description;


    public Spacecraft(){
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPropellant() {
        return propellant;
    }

    public void setPropellant(String propellant) {
        this.propellant = propellant;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}