Error creating a validation in model when i have a before_filter on my controller

I dont know why, but my application run without errors when i dont put the line:     "validates :age, :numericality => true" on my model

if i put that line in the model, this one error appear:

" You have a nil object when you didn't expect it! You might have expected an instance of Array. The error occurred while evaluating nil.map

Extracted source (around line #19):

16: <%= f.text_field :value %> 17: </div> 18: <div class="field"> 19: <%= f.select(:owner_id, options_from_collection_for_select(@owners, :id, :name)) %> 20: </div> 21: <div class="field"> 22: <%= f.select(:reservation_type_id, options_from_collection_for_select(@reservation_types, :id, :name))%>

"

I think that the before_filter is been skipped, but i don't know why or how i could resolve it....

I hope that someone can help me to understand this, and thx.