Weird crystal error

example.cr

f = File.new("buffer_i_gen_batt.txt")

6.times do
  _ = f.gets
end

interval = f.gets

def real_val(raw_val)
  (raw_val - 520) * 0.191
end

def normalize
end

loop do
  break unless n = f.gets

  unless n.to_s == ""
    puts n.to_s.to_i
  end

  # puts n.to_i
end

f = File.new("buffer_i_gen_batt.txt")

6.times do
  _ = f.gets
end

interval = f.gets

def real_val(raw_val)
  (raw_val - 520) * 0.191
end

def normalize
end

loop do
  break unless n = f.gets

  unless n.to_s.strip == ""
    puts n.to_s.strip.to_i
  end

  # puts n.to_i
end

file = File.open("buffer_i_gen_batt.txt")

values = Array(Float64).new

meas_offset = -512
linear_coefficient = 0.191

6.times do
    file.gets
end

interval = file.gets.to_s.to_i
puts interval

file.each_line do |raw_line|
    line = raw_line.to_s.strip
    puts line.inspect
    if line == ""
        raw_value = line.to_i
        real_value = (raw_value + meas_offset) * linear_coefficient
        values << real_value
        puts real_value
    end
end

file.close

min_value = values.min

values.each do |value|
    value -= min_value
end

Stacktrace:

1008
""
invalid Int32:  (ArgumentError)
[4422535] *CallStack::unwind:Array(Pointer(Void)) +87
[4422426] *CallStack#initialize:Array(Pointer(Void)) +10
[4422378] *CallStack::new:CallStack +42
[4390968] *raise<ArgumentError>:NoReturn +24
[4437093] *String#to_i32<Int32, Bool, Bool, Bool, Bool>:Int32 +245
[4436828] *String#to_i:Int32 +92
[4348897] ???
[4400473] main +41
[139764846427973] __libc_start_main +245
[4346921] ???
[0] ???

unless line == "" instead of if

file = File.open("buffer_i_gen_batt.txt")

values = Array(Float64).new

meas_offset = -512
linear_coefficient = 0.191

6.times do
    file.gets
end

interval = file.gets.to_s.to_i
puts interval

file.each_line do |raw_line|
    line = raw_line.to_s.strip
    puts line.inspect
    unless line == ""
        raw_value = line.to_i
        # real_value = (raw_value + meas_offset) * linear_coefficient
        # values << real_value
        # puts real_value
    end
end

file.close

min_value = values.min

values.each do |value|
    value -= min_value
end