570e776a37
- add SCM guidance for deriving base quantities through line unit-of-measure validation`n- add security guidance for parameterizing SetFilter with external text`n- add test isolation guidance for resetting per-test state before initialization guards`n- add web-service guidance for JSON null handling and invariant standard format 9`n- route and cover all five rules with paired evaluation fixtures
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Check for JSON null before converting a value
Description
An optional property in a JSON payload can be missing or present with the value null, and the two cases behave differently in AL. When the Boolean result is captured, JsonObject.Get returns false for a missing key but true for "email": null, because the key exists. The conversion methods on JsonValue (AsText, AsCode, AsDecimal, AsInteger, AsDate, AsBoolean, and the others) fail with a runtime error when the value is NULL or UNDEFINED. Code that guards only with Get therefore passes its tests with the property omitted and fails in production when the sender serializes an empty field as null, which many services do by default.
Best Practice
For every property that the contract allows to be optional or nullable, check three things before converting: that Get (or SelectToken) returned true, that the token IsValue() rather than an object or array, and that AsValue().IsNull() is false. Put this in one small helper per target type and decide explicitly what a missing or null property means: a default, leaving the field unchanged, or a validation error that names the property.
Required properties can still fail fast, but with an error that states the missing or null property instead of a generic conversion error. Keep a numeric or date conversion strict when the contract says the value must be a number or a date; IsNull covers only null, not a value of the wrong type.
See sample: check-json-null-before-converting-values.good.al.
Anti Pattern
if Json.Get('email', Token) then Email := Token.AsValue().AsText(); or an unguarded Token.AsValue().AsDecimal() on a property that the external contract allows to be null. The Get check makes the code look defensive, but it doesn't handle a present null. Detection signal: an As<Type>() call on a JsonValue obtained from an external payload with no preceding IsNull() check on the same token, where the property isn't documented as always non-null.
See sample: check-json-null-before-converting-values.bad.al.