FATAL_ERROR System.QueryException: List has no rows for assignment to SObject

Question

I have taken a reference from : https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/pages_controller_custom.htm and developed below code.

But it gives me the following error.

FATAL_ERROR System.QueryException: List has no rows for assignment to SObject

MyController

public class MyController {
    private final Account account;

    public MyController(){
        Id newId = ApexPages.currentPage().getParameters().get('id');
        System.debug('New ID : '+newId);
        account = [SELECT Id, Name, Site FROM Account WHERE Id = :newId];
    }

    public Account getAccount(){
        return account;
    }

    public PageReference save(){
        update account;
        return null;
    }
}

MyControllerVF

<apex:page controller="MyController" tabStyle="Account">
    <apex:form>
        <apex:pageBlock title="Congratulations {!$User.FirstName}">
            You belong to Account Name: <apex:inputField value="{!account.name}"/>
            <apex:commandButton action="{!save}" value="save"/>
        </apex:pageBlock>
    </apex:form>
</apex:page>

My input screen.

Answer 1

EDIT added upsert + exception handling

This is not going to fix the problem - while the error checking is good, it won't prevent the error mentioned here from occurring.

You shouldn't query straight to a single sObject - you need to query to a list. Eg:

Account[] accounts = [SELECT Id, Name, Site FROM Account WHERE Id = :newId];
if (!accounts.isEmpty()){
  account = accounts[0];
}
else {
  account = new Account();
}

Then your save method can upsert the Account.

public PageReference save(){
  try {
    upsert account;
    return null;
  }
  catch (Exception e){
    ApexPages.addMessage(new ApexPages.Message(
      ApexPages.Severity.Error, 
      'Line ' + e.getLineNumber() + ' ' + e.getMessage()
    )); 
  }
  return null;
}

Answer 2

You should always query in a List like:

Id newId = ApexPages.currentPage().getParameters().get('id');
System.debug('New ID : '+newId);
if (newId == NULL) { 
    ApexPages.addMessage(new ApexPages.Message(
        ApexPages.Severity.Error, 
        System.Label.UnabletoFindIdParameter // make sure to create the custom label
    )); 
} else {
    List<account> accounts = [SELECT Id, Name, Site FROM Account WHERE Id = :newId];
    if(accounts.size() > 0){
        /* We got record from database process it using accounts[0] */
    }else{
        /* No record found with the Id provided in the URL. */
    }
}