Fix All Bugs in Code

Nextcapital models employer 401(k) matching, where the employer matches a percentage of what an employee contributes, tiered by how much of their salary they're contributing. The tiers describe bands as a percentage of salary — for example, "match 100% of contributions up to 3% of salary, then 50% of contributions on the next 2%." This method is supposed to compute the total dollar match for one employee, but the numbers it's producing don't line up with the plan documents.

def employer_match(salary, contribution_rate, match_tiers)
  employee_contribution = salary * contribution_rate

  match_total = 0
  match_tiers.each do |tier|
    if employee_contribution > tier[:up_to]
      match_total += tier[:up_to] * tier[:rate]
    else
      match_total += employee_contribution * tier[:rate]
    end
  end

  match_total
end

match_tiers looks like [{ up_to: 0.03, rate: 1.0 }, { up_to: 0.05, rate: 0.5 }], where up_to is a fraction of salary and rate is the employer's match rate for that band. Fix all the bugs in this method. Explain each one and how it produces a wrong dollar figure, since this feeds directly into what employees see as their expected match.