TypeError in Devise::RegistrationsController#create - ruby-on-rails

Question

For Devise with Rails 4.2., I am able to sign up users when I turn off confirmation required in my user model but when I turn it back on I get this error.
no implicit conversion of Array into String <
# i.e. OpenSSL::Digest::SHA1#block_length
def generate_key(salt, key_size=64)
OpenSSL::PKCS5.pbkdf2_hmac_sha1(#secret, salt, #iterations, key_size)
end
end
referring to this line
devise (3.5.10) lib/devise/token_generator.rb:50:in `pbkdf2_hmac_sha1'
I am using mailtrap for my development settings and I am able to get mail in my contact page.
In my user.rb I have
devise :database_authenticatable, :registerable,
:recoverable, :rememberable, :trackable, :validatable, :confirmable
My devise initalizer is set exactly the same as another project that works.
In my application controller, I have set parameters
before_action :configure_permitted_parameters, if: :devise_controller?
def configure_permitted_parameters
devise_parameter_sanitizer.for(:sign_up) { |u| u.permit(:firstname, :lastname, :email, :avatar, :password, :password_confirmation) }
end
My views/devise contain the folders (confirmations, mailer, passwords, registrations, sessions, shared, and unlocks.
My devise registrations new is below:
<div class="row">
<%= bootstrap_devise_error_messages! %>
<div class="panel panel-default devise-bs">
<div class="panel-heading">
<h4><%= t('.sign_up', :default => "Sign up") %></h4>
</div>
<div class="panel-body">
<%= form_for(resource, :as => resource_name, :url => registration_path(resource_name), html: { role: "form" }) do |f| %>
<div class="form-group">
<%= f.label :firstname %>
<%= f.text_field :firstname, autofocus: true, class: "form-control" %>
</div>
<div class="form-group">
<%= f.label :lastname %>
<%= f.text_field :lastname, autofocus: true, class: "form-control" %>
</div>
<div class="form-group">
<%= f.label :email %>
<%= f.email_field :email, autofocus: true, class: "form-control" %>
</div>
<div class="form-group">
<%= f.label :avatar %><br>
<%= f.file_field :avatar, autofocus: true, class: "form-control" %>
</div>
<div class="form-group">
<%= f.label :password %>
<% if #minimum_password_length %>
<em>(<%= #minimum_password_length %> characters minimum)</em>
<% end %><br />
<%= f.password_field :password, autocomplete: "off", class: "form-control" %>
</div>
<div class="form-group">
<%= f.label :password_confirmation %>
<%= f.password_field :password_confirmation, autocomplete: "off", class: "form-control" %>
</div>
<%= f.submit t('.sign_up', :default => "Sign up"), class: "btn btn-primary" %>
<% end %>
</div>
<div class="panel-footer">
<%= render "devise/shared/links" %>
</div>
</div>
Any tips on what I could be doing wrong, I have spun my wheels for a couple of days.
Thanks :)

Answer 1

Check that your to_json/as_json in your user.rb is working properly.