Added BC break to hide empty xml tags from json version

[DracoBlue]

Source:

<root>
    <zerovalue></zerovalue>
    <zerovalue>hans</zerovalue>
    <zerovalue></zerovalue>
    <zerovalue>hans2</zerovalue>
    <zerovalue></zerovalue>
</root>

Craur 2.x:

$node->get('root.zerovalue[]') === [null, "hans", null, "hans2", null];

Craur 3.x

$node->get('root.zerovalue[]') === ["hans", "hans2"];