Enricher

INT-3465:Content Enricher Improvements
Logically it is a wrong place for the `null-result-expression`: you start for the `valueProcessorBuilder`, but then switch to `nullResultHeaderExpression`. In the end you again come back to the `valueProcessorBuilder`.
From other side we should cover this case:
````xml
<header name="foo" null-result-expression="'bar'"/>
````
Where there is no `value`, neither `expression`. Hence, we shouldn't populate `valueProcessorBuilder` to the `expressions`. We have only `nullResultValueProcessorBuilder` for the `nullResultHeaderExpressions`.

Actually, the same for `<property>`