Validation fails with select option list

I have a form with some text_field and some drop down lists.



Program:


<%= options_from_collection_for_select @programs, “id”, “prg_name”,
@student.program_id %>

I am not able to use validates_presence_of in the model whenever I am
including this options_from_collection_for_select list. If I remove that
it checks for the presence of the field. Otherwise, it gives me the
following error
You have a nil object when you didn’t expect it!
You might have expected an instance of Array.
The error occured while evaluating nil.inject

Extracted source (around line #18):

17:

Program:

18: <%= options_from_collection_for_select @programs, “id”,
“prg_name”, @student.program_id %>
19:
20:
21:

What is the reason for this?

Any help appreciated.
Thanks
Silvy Mathews