How to Catch an "Undefined Method '[]' for Nil:Nilclass" Error

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

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.

Ruby: undefined method `' for nil:NilClass error message

@students refers to an empty array.

Does it? (Apparently not, because the error message says it's nil!!) You never showed us where this variable get initialised.

In ruby, all instance variables evaluate to nil by default, if you don't define them as something else.

Undefined method for NilClass

In your first loop iteration new_matrix[h_entries] would be nil. So, you can't use << method on it.

Try to initialize it to an empty array if it is nil:

new_matrix[h_entries] ||= []
new_matrix[h_entries] << ([array[h_entries][v_entries]])

Undefined method `%' for nil:NilClass (NoMethodError)

The elements of range are 1 to 100, but the indices into range are 0 to 99. The each method already gives you the elements of the array, not the indices — just use i inside the loop body instead of range[i].

You would have gotten a more reasonable error if you indexed an array a with a.fetch(i) instead of a[i] — the former throws IndexError while the latter gives nil.

How to catch an undefined method `[]' for nil:NilClass error?

A bit late to the party, but, as pointed in this answer, Ruby 2.3.0 introduced a new method called dig, which would return nil if one of the chained keys is nil. Your omniauth auth hash could then be presented as:

omniauth = { 
            ...                 
            "extra"=>{ "raw_info"=>
                        { "location"=>"New York",
                          "gravatar_id"=>"123456789"}}
             ...
           }

omniauth.dig('extra', 
             'raw_info',
             'location',
             'name',
             'foo',
             'bar',
             'baz') #<= nil

Undefined method `+' for nil:NilClass (NoMethodError)

Local variable reference has precedence over method call with the same name.

Similarly, local variable assignment has precedence over method call with the same name. A writer method of the form foo= needs an explicit receiver. When the receiver is omitted, it is not recognized as a method, but as a local variable assignment.

def add_cash(amount)
  self.cash = cash + amount
end

Why do I get undefined method for nil:NilClass on an object that clearly exists?

I'm pretty sure that the record you inspect (Daily with id=1030) and the failing [non-existing] record are two different records. Here's how you can find out. Amend your method like this, temporarily:

def daily_data_for(store, month, day, year, field)
  daily = Daily.where(store_id: store, month: month, day: day, year: year).first
  raise "Daily not found for #{store.inspect}, #{month.inspect}, #{day.inspect}, #{year.inspect}" unless daily
  daily.send(field)
end

Now the error message should be much more revealing.

undefined method `errors' for nil:NilClass in rails

You are using nested routes but in form_with you have not specified that. Try to change the form_with like this:

form_with(model: stage, url: [@project, stage])

Source: https://stackoverflow.com/a/46919792/4207394

You will have to check the variable names, i.e., the stage variable should have the new Stage object and @project variable should have the Project object or else please change the names accordingly.

undefined method `-' for nil:NilClass in ruby model

You can't call or chain methods on a nil object. You're trying to subtract something from nil which the error has told you. So you can fix this with:

def seat_avaliable
  if seat.is_a?(Integer) && students&.any?
    seat - students.count > 0
  end
end

Change your view code to this

<% if bus.seat_available %><td>Seat Available</td><% end %>

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