Quick Answer

Common error when calling methods on nil values.

Understanding the Issue

This occurs when a variable is nil and you try to call a method on it. Always check for nil or use safe navigation.

The Problem

This code demonstrates the issue:

Ruby Error 
# Problem: Nil reference
user = find_user(id)
user.name # Error if user is nil

The Solution

Here's the corrected code:

Ruby Fixed 
# Solution 1: Check nil
user.name if user

# Solution 2: Safe navigation (Ruby 2.3+)
user&.name

# Solution 3: Null object pattern
class NullUser
  def name
    "Guest"
  end
end
user || NullUser.new

Key Takeaways

Always handle nil cases defensively.