Catch Nil Error in If/Else

While this seems beyond simple to me, I caot seem to figure out how to code this. I am trying to write an if/else if/else statement, but it's not working. Here's what I have:

for value in values {
  if Float(value) > 0 {
    print("positive")
  } else if value == "N/A" {
    print("not available")
  } else {
    print("negative")
  }
}

Values is an array of strings, where the value is either "1.0", "N/A", or "-1.0". Through array iteration, if it hits "N/A", it throws an error. I feel like I need to embed this in a try/catch block. It's catching a nil error. Thanks!