BIGIP throws syntax error for iRule upon upgrading f5 to 12.x for below : set given_context_path [string trimright [URI::path [HTTP::uri] 1 1] "/"]

BIGIP throws syntax error for iRule upon upgrading f5 to 12.x for below :

set given_context_path [string trimright [URI::path [HTTP::uri] 1 1] "/"]

The below warnings logged in BIGIP seems to be occurring as F5 has been upgraded from version 11.x to 12.x, which doesn't support the syntax used in previous version. Prior to 12.0.0 there were no restrictions to the values of the arguments specified. However, In 12.x version, JET validator engine has been introduced which performs more stringent iRules syntax validation by using JET files during configuration load. 

warning: [The following errors were not caught before. Please correct the script in order to avoid future disruption. "end value (1) not greater than start value (1)"193 25][URI::path [HTTP::uri] 1 1]

It looks like the form of URI::path with same start and finish values is set to be deprecated in a future release, and while the parser is allowing it now, it's warning about this usage.

Could you please suggest me the correct syntax for this.