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_Expressions_

# Conditional Fields

Field comprehensions can also be used to
add a single field conditionally.

Converting the resulting configuration to JSON results in an error
as `justification` is required yet no concrete value is given.


<!-- CUE editor -->
_conditional.cue:_
```
price: number

// Require a justification if price is too high
justification: string if price > 100

price: 200
```

<!-- result -->
`$ cue eval conditional.cue`
```
price:         200
justification: string
```