i have the problem in MainActivit when open for fist or when open the MainActivity without click on listView in second Activity

i have problem with Intent in Android...

in my project i have 2 Activity...the Main ACTYVITY and the second activity...

In second Activity i have one ListView and when i click to lis,t go to in MainActivity for show the result row...

but i have the problem in MainActivit when open for fist or when open the MainActivity without click on listView in second Activity;

This is the code of MainActivity:

import com.example.karlive.Book;  
import com.example.karlive.DataHelper;  
 
import android.os.Bundle;  
import android.app.Activity;  
import android.content.Intent;  
import android.view.Menu;  
import android.view.View;  
import android.widget.Button;  
import android.widget.TextView;  
 
public class MainActivity extends Activity {  
 
 
    @Override 
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
          
        TextView nomeTextView = (TextView)findViewById(R.id.link_nome);  
          
          
 
            //  THE PROBLEM IS HERE!!!!!!!    
            DataHelper dh = new DataHelper(this);  
            Intent intent = getIntent();  
            String bookName = (String) intent.getSerializableExtra("bookName");  
            final Book book = dh.getBookDetails(bookName);  
              
            nomeTextView.setText(book.getNome());  
 
        //}  
          
          
          
        Button list = (Button)findViewById(R.id.list);  
        list.setOnClickListener(new View.OnClickListener() {  
            @Override 
            public void onClick(View v) {  
                // TODO Auto-generated method stub  
                Intent intent = new Intent();  
                intent.setClass(getApplicationContext(), Lista.class);  
                startActivity(intent);  
            }  
        });  
        Button database = (Button)findViewById(R.id.database);  
        database.setOnClickListener(new View.OnClickListener() {  
            @Override 
            public void onClick(View v) {  
                // TODO Auto-generated method stub  
                Intent intent = new Intent();  
                intent.setClass(getApplicationContext(), Database.class);  
                startActivity(intent);  
            }  
        });  
    }  
 
 
 
} 
import com.example.karlive.Book;
import com.example.karlive.DataHelper;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  
  TextView nomeTextView = (TextView)findViewById(R.id.link_nome);
  
  

   //  THE PROBLEM IS HERE!!!!!!!  
   DataHelper dh = new DataHelper(this);
   Intent intent = getIntent();
   String bookName = (String) intent.getSerializableExtra("bookName");
   final Book book = dh.getBookDetails(bookName);
   
   nomeTextView.setText(book.getNome());

  //}
  
  
  
  Button list = (Button)findViewById(R.id.list);
  list.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    Intent intent = new Intent();
             intent.setClass(getApplicationContext(), Lista.class);
             startActivity(intent);
   }
  });
  Button database = (Button)findViewById(R.id.database);
  database.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    Intent intent = new Intent();
             intent.setClass(getApplicationContext(), Database.class);
             startActivity(intent);
   }
  });
 }

}

The problems is when open the MainActivity...
import com.example.karlive.Book;  
import com.example.karlive.DataHelper;  
 
import android.os.Bundle;  
import android.app.Activity;  
import android.content.Intent;  
import android.view.Menu;  
import android.view.View;  
import android.widget.Button;  
import android.widget.TextView;  
 
public class MainActivity extends Activity {  
 
    TextView nomeTextView,;  
    @Override 
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main );  
          
        nomeTextView = (TextView)findViewById(R.id.link_nome);  
          
          
          
                  
            DataHelper dh = new DataHelper(this);  
            Intent intent = getIntent();  
            String bookName = (String) intent.getSerializableExtra("bookName");  
            final Book book = dh.getBookDetails(bookName);  
              
            nomeTextView.setText(book.getNome());  
            baseTextView.setText(book.getBase());  
          

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