```ruby
name :bmi
require_helpers :get_field_as_float

execute do
  weight = get_field_as_float :weight_in_kg
  height = get_field_as_float :height_in_m

  fail FieldError.new('weight', 'must be greater than zero') if weight <= 0
  fail FieldError.new('height', 'must be greater than zero') if height <= 0

  {
    value: weight / (height ** 2),
    units: "kg/m^2"
  }
end
```

Remove unnecessary spaces and use single quotes for units
user
```ruby
name :bmi
require_helpers :get_field_as_float

execute do
  weight = get_field_as_float :weight_in_kg
  height = get_field_as_float :height_in_m

  fail FieldError.new('weight', 'must be greater than zero') if weight <= 0
  fail FieldError.new('height', 'must be greater than zero') if height <= 0

  {
    value: weight / (height**2),
    units: 'kg/m^2'
  }
end
```
assistant