fix this error

[sociliza]

undefined method `accept!' for nil:NilClass

[eblohm]

What version of the gem are you using?

[sungwoncho]

@sociliza Possibly related to #25. Need gem version and steps to reproduce.

[Advice-Dog]

I was able to reproduce this issue while attempting to use link_to.
has_friendship 1.0.2 with devise 4.2.0

// users/show.html.erb
<%= link_to 'Accept Friend Request', current_user.accept_request(@user) %>

I think it's because I'm trying to use this incorrectly. Can you add an example using link_to to the ReadMe?
Also, can you also add an example about checking if there is a sent pending request towards that user? I only saw friends_with?.