I'm posting a piece of before insert/ update trigger, it has to populate custom email field on Opportunity into Account's Email custom field. 

I'm trying to do something like this:

> 
> 
> 

```
For(Opportunity opp : trigger.new)
     { 
       If(!SetEmaiIDs.contains(opp.Email__c)) // checking if added email is already not present on some other account
       {
         opp.Account.Account_Email__c  = opp.Email__c; // This line is throwing error

       }

```

Seems like this line 'opp.Account.Account\_Email\_\_c' is not working 
Can't we access account field like above , it is giving 
Attempt to de-reference a null object: error on same line

Thanks !