Paperclip Giving Required field error

in my project i have form in that there is file field to upload file and I am using paperclip gem for that and add only validation 'validates_attachment_content_type' but when i submit a form without any file selected it gives error of 'validates_a开发者_JAVA百科ttachment_content_type', it should not give any error as i am not add validation 'validates_attachment_presence'. I am very confused for what it giving error of 'validates_attachment_content_type' when i submit a form without any file uploaded.

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after googling for the same i got answer for this prob just we have to add :allow_nil => true in validation

for eg.

validates_attachment_content_type :logo, :content_type => ['image/jpeg','image/png','image /jpg','image/gif'], :message=>"Image file must be of .jpeg,'.jpg', '.gif' or .png type",:allow_nil => true

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:allow_nil => true

is realy work great and very easy to test.YOu can put it after your validation.