Could not find a valid mapping for nil - ruby-on-rails

Question

So, I'm using carrier wave to allow users to upload profile images. Now ultimately, I'd like the user to be able to click on the image and upload a new one on the fly in the profile.html.haml page.
So, I've tried the below adding a form with a put action to let the user update the image on the fly without having to go to the edit.html.haml page.
However, I'm being hit with this error:
Could not find a valid mapping for nil
Extracted source (around line #8):
<%= form_for(#user, :url => registration_path(#user), :html => { :method => :put }, :html => {:multipart => true}) do |f| %>
<%= link_to (image_tag current_user.profile_image_url(:thumb).to_s), edit_account_path(current_user)%>
<% end %>
Where did I go wrong?
Alternatively I've tried this which might be totally off:
<%= link_to (image_tag current_user.profile_image_url(:thumb).to_s), f.file_field :profile_image%>
which gave this error:
Sites/Friendiose-master/app/views/home/landing_welcome.html.erb:9: syntax error, unexpected tSYMBEG, expecting ')'
...l(:thumb).to_s), f.file_field :profile_image);#output_buffer...
Thanks in advanced.

Answer 1

So firstly, what do you think this error might me. Most common errors ever:
Sites/Friendiose-master/app/views/home/landing_welcome.html.erb:9: syntax error, unexpected tSYMBEG, expecting ')'
...l(:thumb).to_s), f.file_field :profile_image);#output_buffer...
I'm not going to give you full answer but teach you to think how you can debug it.
https://github.com/carrierwaveuploader/carrierwave
That is the documentation for carrierwave. When showing the image it says the following:
<%= form_for #user, :html => {:multipart => true} do |f| %>
<p>
<label>My Avatar</label>
<%= image_tag(#user.avatar_url) if #user.avatar? %>
<%= f.file_field :avatar %>
<%= f.hidden_field :avatar_cache %>
</p>
<% end %>
One tip and this is not me being sarcastic but get used to reading alot and googling even more. I haven't used paperclip but I can see the issues from 2 mins googling.
Ruby on Rails using link_to with image_tag
There is how to create a link with an image.
From that link look at the difference between yours:
<%= link_to (image_tag current_user.profile_image_url(:thumb).to_s), edit_account_path(current_user)%>
and the correct way:
<%=link_to( image_tag(participant.user.profile_pic.url(:small)), user_path(participant.user), :class=>"work") %>
What does the error say you are missing?
It is not always great to give people an answer straight away but the keys on how to figure it out.