Magik.Validator.validate_required

You're seeing just the function validate_required, go back to Magik.Validator module for more information.
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validate_required(value, func)

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Validate value if value is not nil. This function can receive a function to dynamicall calculate required or not.

iex(1)> Magik.Validator.validate_required(nil, true)
{:error, "is required"}
iex(2)> Magik.Validator.validate_required(1, true)
:ok
iex(3)> Magik.Validator.validate_required(nil, false)
:ok
iex(4)> Magik.Validator.validate_required(nil, fn -> 2 == 2 end)
{:error, "is required"}