Forum OpenACS Q&A: Error thrown by Xowiki when entering field of type 'URL'

can't read "expr": no such variable
while executing
"regexp -nocase $expr $value"
(procedure "check=safe_url" line 3)
::xotcl::__#C ::xowiki::formfield::url->check=safe_url
invoked from within
"my $validator_method $value"
(procedure "validation_check" line 2)
::xotcl::__#C ::xowiki::formfield::FormField->validation_check
invoked from within
"my validation_check $validator_method $value"
(procedure "validate" line 26)
::xotcl::__#C ::xowiki::formfield::FormField->validate
invoked from within

Has anyone seen this before?

URL entered was:
https://erm.navtech.aero/AEROCHART/ShowNotam.aspx?icao=EGLL