Error comparing Array in IF

This is my code

v3 = []
w=j=k=0
puts "Digite o tamanho do vetor 1"
m = gets.to_i
v1 = Array.new(m)
puts "Digite o tamanho do vetor 2"
n = gets.to_i
v2 = Array.new(m)

for i in 0..m-1
    puts "Digite os valores do vetor 1: "
    v1.push(gets.to_i)
end
for i in 0..n-1
    puts "Digite os valores do vetor 2: "
    v2.push(gets.to_i)
end

while w <= m+n-1
    if (v1[j] < v2[k])
        v3.push(v1[j])
        j += 1
    elsif (v1[j] = v2[k])
        v3.push(v1[j])
        j = j +1
        k = k +1
    else
        v3.push(v2[k])
        k = k +1
    end
    w+=1
end

But it's the error when comparing v1[j] < v2[k]

Error returned:

:20:in '<main>': undefined method '<' for nil:NilClass (NoMethodError)