TypeError: nil can't be coerced into Integer Ruby / Rails Origin: Application & API Last updated 5 Nov 2026

Ruby: TypeError: nil can't be coerced into Integer / String can't be coerced into Integer

Arithmetic combined a number with nil (or a String) which Ruby can't convert automatically.

Exact message you may see TypeError: nil can't be coerced into IntegerTypeError (nil can't be coerced into Float)String can't be coerced into IntegerTypeError (String can't be coerced into Integer)nil can't be coerced into BigDecimal
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Seen on: Ruby

Meaning

A variable or column used in +, *, sum is nil. Default values (to_i, || 0, .to_f), DB defaults (null: false, default: 0), and parsing params (Integer(params[:n], exception: false)) fix it. "5" + 1 gives "no implicit conversion", while 1 + "5" gives "String can't be coerced".

Common causes

  • nil attribute used in arithmetic
  • String from params not converted
  • sum over nil elements
  • Missing DB default
  • Operand order (1 + nil)

⚡ Quick fix

  1. `(value
  2. 0) + 1 or value.to_i`
  3. Add DB defaults and null: false
  4. compact.sum for arrays with nil

Detailed fix by platform

Ruby

  1. total = items.map { |i| i.price.to_f }.sum

How to diagnose

  1. Operand — Which is nil?
  2. Source — Param/DB?
  3. Default — Provided?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Application & API. Errors that are often confused with or caused by this one (click to open):

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