ActionController::ParameterMissing

ActionController::ParameterMissing is raised when using require() on params and the required key is missing. This is part of Rails strong parameters.

Common causes

• Form submitted without required nested params
• API request missing required body
• Wrong parameter key name in form
• JavaScript disabled preventing form submission
• CSRF token issues causing form data loss

How to fix it

• Verify form field names match expected params
• Use permit with fetch for optional nested params
• Add proper error handling for missing params
• Validate params presence before require
• Check form_with model naming conventions

Example

# Error example
def user_params
  params.require(:user).permit(:name, :email)
end
# If params = {} => ActionController::ParameterMissing: param is missing or empty: user

# Fix with conditional check
def user_params
  if params[:user].present?
    params.require(:user).permit(:name, :email)
  else
    {}
  end
end

# Or rescue in controller
rescue_from ActionController::ParameterMissing do |e|
  render json: { error: e.message }, status: :bad_request
end

Related errors