appendMissingElements property

Append the given elements in order if they are not already present in the current field value.

If the field is not an array, or if the field 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 Null is equal to Null. If the input contains multiple equivalent values, only the first will be considered. The corresponding transform_result will be the null value.