Ruby: undefined method `[]' for nil:NilClass when trying to get Enumerator on an Array of Hashes

Question

I am trying to loop on an Array of Hashes. When I reach the point where I fetch the Enumerator to start looping, I get the following error:

undefined method `[]' for nil:NilClass

My code looks like the following:

def extraireAttributs (attributsParam)
  classeTrouvee = false
  scanTrouve = false
  ownerOSTrouve = false
  ownerAppTrouve = false
  resultat = Hash.new(0)
  attributs = Array(attributsParam)

  attributs.each do |attribut| #CRASHES HERE!!!
    typeAttribut = attribut['objectTypeAttribute']
    [...]

I checked in debug mode to make sure the attributsParamsargument and the attributsvariable are not nil or empty. Both (because they are the same!) contain 59 Hashes objects, but I still cannot get an Enumerator on the Array.

Why do I keep on getting this error?

Thanks!

Solution

undefined method `[]' for nil:NilClass says you tried to do something[index] but something is nil. Ruby won't let you use nil as an array (ie. call the [] method on it).

The problem is not on the attributs.each line but on the line following which calls the [] method on attribut.

typeAttribut = attribut['objectTypeAttribute']

This indicates something in attributs is nil. This could happen if attributsParam is a list that contains nil like so.

attributsParam = [nil];
attributs = Array(attributsParam);

# [nil]
puts attributs.inspect

Simplest way to debug it is to add puts attributs.inspect just before the loop.

Also consider if you really need the attributs = Array(attributsParam) line or if it's already something Enumerable.

Comments

[Joe Toug]

You are right. The inner structure of the hashes which are inside the outer array have changed. Therefore the exception happened inside the loop. Thanks a lot!