Evaluate Variable value containing expression language

Evaluate Variable value containing expression language

I loaded custom properties into nifi.

The registry variable called query has value "SELECT * FROM table WHERE id = ${id_no}" where the id_no is coming from the flowfile attributes. There was no functionality in nifi to evaluate the expression language inside the value.

So, need to add functionality such that we can evaluate EL inside the variables.

example: ${query:stringEl}

where function `stringEl` will evaluate the EL value inside the query variable