How to isolate a specific url parameter from my query string

[robinl39529461]

Hi, 
In the mapping of my datastream, I want to isolate the value of a specific url parameter.
Example: from "test=1&account=bitmap&step=abc", I want to map as output the value of account, so 'bitmap' in this case.

I did it this way based on this doc and it works:

But I have also unwished value if the parameter contains 'account=', not only equals 'account='

Example:

Output should be null because the parameter name is 'IDaccount=' and not 'account='.

Any idea how I can fix this ?

Thanks

Robin