appendMissingElements property
Appends the given elements in order if they are not already present in the current property value.
If the property is not an array, or if the property does not yet exist, it is first set to the empty array. Equivalent numbers of different types (e.g. 3L and 3.0) are considered equal when checking if a value is missing. NaN is equal to NaN, and the null value is equal to the null value. If the input contains multiple equivalent values, only the first will be considered. The corresponding transform result will be the null value.
Implementation
ArrayValue? appendMissingElements;