The Problem

I recently ran into this bug during a code review. In an attempt to avoid long chains of or statements, code like the following was introduced:

if [
  some_model.nil?,
  some_model.some_attr,
  # ...
].any?
  return false
end

It is simple to understand the intent, however, errors like the following started to appear:

NoMethodError: undefined method `some_attr' for nil:NilClass

The Cause

At first glance, it appears that Array#any? is not short-circuiting. In reality, any? can short-circuit, but the array elements are evaluated before any? runs, so some_model.some_attr is still called even when some_model.nil? is true.

The Solution

The problem here occurs because we expected an earlier condition in the same expression to protect us from errors in a later condition. There are many ways to avoid this.

One could use || statements:

if some_model.nil? || some_model.some_attr # || ...
  return false
end

One could use nil-safe attribute accessors:

if [
  some_model.nil?,
  some_model&.some_attr,
  # other chained conditions..
].any?
  return false
end

In the end, I've come to prefer using || statements. Using #any? here makes it more likely that bugs may sneak in if the writer or reviewer is unfamiliar with this nuance, or if tests do not cover the condition. Keeping it simple with || is clearer and avoids this language-specific gotcha.