Using [<filter_expression>]
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[<filter_expression>] has been added to extend the @select attribute syntax. It returns a Boolean value that determines whether or not property should be added to the result. Use square brackets to define <filter_expression> after an explicit property name or “*”.
is_not_null() is the only valid filter expression used in AML.
select=”*[is_not_null()]” means: add all properties into the response if property value is NOT NULL.
<Item type="A1" action="get” />
is equivalent to
<Item type="A1" action="get” select="*[is_not_null()]"/>