Lỗi Unfortunately,application has stopped. khi run app android?

Mình mới học Java/Android có làm demo app chuyển đổi các giá trị đo lường,mới làm được với nhiệt độ thì có lỗi xử lý event button,đây là code ở layout và activity của mình :

<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/rlPanel"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#ff008200"
    tools:context=".MainActivity">


    <TextView
        android:id="@+id/tvTempPanel"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Convert Temperature"
        android:gravity="center"
        android:textSize="36dp"
        android:layout_marginTop="30dp"
        android:layout_marginBottom="30dp"/>


    <EditText
        android:id="@+id/etTemp"
        android:layout_below="@+id/tvTempPanel"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:inputType="number"
        android:text=""
        android:gravity="center_horizontal"
        android:paddingLeft="10dp"
        android:paddingRight="10dp"
        android:textColorHint="#ffff8d75"/>
    <RadioGroup
        android:id="@+id/radioGroup"
        android:layout_below="@+id/etTemp"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:orientation="vertical">

        <RadioButton
            android:id="@+id/rbtnF"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Fehrenheit to Celcius"/>

        <RadioButton
            android:id="@+id/rbtnC"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="Celcius to Fehrenheit"/>

    </RadioGroup>

    <LinearLayout
        android:id="@+id/layout2Temp"
        android:layout_below="@+id/radioGroup"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center_horizontal"
        android:layout_marginTop="30dp"
        android:layout_marginBottom="30dp"
        android:orientation="horizontal">

        <Button
            android:id="@+id/btnConvert"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Convert"/>

        <Button
            android:id="@+id/btnClear"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Clear"/>

    </LinearLayout>

    <TextView
        android:id="@+id/tvTempResult"
        android:layout_below="@+id/layout2Temp"
        android:layout_marginTop="30dp"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text=""
        android:gravity="center"
        android:textSize="24dp"/>

</RelativeLayout>

và activity :

package com.example.legend.myapplication;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.RadioButton;
import android.widget.TextView;
import android.widget.Toast;


public class MainActivity extends ActionBarActivity {

    private Button btnConvert,btnClear;
    private EditText etTemp;
    private RadioButton tempF,tempC;
    private TextView tvTempResult;

    private View.OnClickListener myVarListener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            if(v==btnConvert){
                if(etTemp.getText()!=null){
                    if(tempF.isChecked()){
                        float f=Float.parseFloat(etTemp.getText().toString());
                        float c=(f-32)*(float)5/9;
                        tvTempResult.setText(String.valueOf(f) +" Fehrenheit = "+String.valueOf(c)+ " Celcius");
                    }
                    else if(tempC.isChecked()){
                        float c=Float.parseFloat(etTemp.getText().toString());
                        float f=c*(float)9/5 +32;
                        tvTempResult.setText(String.valueOf(c) +" Celcius = "+String.valueOf(f)+ " Fehrenheit");
                    }
                    else {
                        Toast.makeText(MainActivity.this,"Please mark an unit",Toast.LENGTH_LONG).show();
                    }
                }else {
                    Toast.makeText(MainActivity.this,"Please input data",Toast.LENGTH_LONG).show();
                }

            }else{
                etTemp.setText("");
                etTemp.requestFocus();
            }
        }

    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnConvert=(Button)findViewById(R.id.btnConvert);
        btnClear=(Button)findViewById(R.id.btnClear);
        etTemp=(EditText)findViewById(R.id.etTemp);
        tempF=(RadioButton)findViewById(R.id.rbtnF);
        tempC=(RadioButton)findViewById(R.id.rbtnC);
        tvTempResult=(TextView)findViewById(R.id.tvTempResult);
        btnConvert.setOnClickListener(myVarListener);
        btnClear.setOnClickListener(myVarListener);
    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }
}

nếu như để ở editText null và mark vào 1 radio button thì có lỗi xảy ra,mình nghĩ là nó ko thực thi được ở lệnh else(etTemp.getText()==null) nhưng không biết xử lý sao cả,mong mọi người chỉ giúp.