undefined method `+' for nil:NilClass

I'm trying to send emails in my application.
the email function in under the ActionMailer::Base as follows:

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def xxxxx(aaa, recipient, bbb, burl)
   @from = aaa.email
   @recipients = [ recipient ]
   @subject = "#{aaa.firstname} #{aaa.lastname} has emailed U!"
   @content_type = "text/plain"

   @body["aaa"] = aaa
   @body["bbb"]= bbb
   @body["uri"] = "#{burl}subscribe/welcome/#{bbb.id}";
end

-------------------------------------------------------------------------

It's email template is:

Hi,

<%= @aaa.firstname %> <%= @aaa.lastname %> has wants to discuss: '<%=
@bbb.name %>'.

Click here: <%= @uri %> .

Best regards,
The MySite Team
-------------------------------------------------------------------------

When i execute these i get this error "undefined method `+' for
nil:NilClass".
Kindly help me out to overcome this issue!

It would help to know what line/file that error is happening on.

I'm gonna guess since I don't see a '+' anywhere in the above code that the model for @bbb has a 'name' method which looks something like:

def name
   self.firstname + self.lastname
end

And I'm guessing that @bbb is nil.

But without knowing where the actual error occured it's hard to say...

-philip