Evaluates the given EL {{expression}} with {{*variables}}, and this fails if the evaluation is not {{null}}.

The variable identifiers are {{$1}}, {{$2}}, {{$3}} ... and so on depending on the number.

*Note:* The {{*variables}} can be an EL expression as well.

Example:

| `EL Add Variable`    | nullVar    | $[null]  |
| `EL Should Be Null`  | $[null]    |
| `EL Should Be Null`  | $[$1]      | $[null]  |
| `EL Should Be Null`  | $[nullVar] |

See also `EL Should Not Be Null`.