Bk citool with file name \' creates Tcl error

I get a Tcl error from bk citool if I click on a file named ’ (tick). Yes, that is a valid file name on Unix file systems:

The Tcl error message is:

cannot write to undefined hash index
    while executing
    (procedure "bk" line 174)
    invoked from within
"comments = bk("cfile print '${sf.file}'")"
    (procedure "getCommentsFromDisk" line 1907)
    invoked from within
"self.comments = getCommentsFromDisk(sf)"
    (procedure "selectFile" line 1283)
    invoked from within
"selectFile item1"
    (command bound to event)

How to reproduce:

touch \'
bk citool \'

…and click on the new file.

I’m using bk 7.3.3:

# bk version
BitKeeper version is bk-7.3.3 for x86_64-glibc213-linux
Built by: wscott@debian70-64.bitkeeper.com in /build/dev-oss-wscott/src
Built on: Sat Dec 29 2018 13:23:45 CET (12 months ago)
Running on: x86_64-glibc213-linux,5.3.15-300.fc31.x86_64

Nice bug report.
I am not the TCL guy, but you can see why in the backtrace. On line 1907 it is building a command line where it is quoting the argument with single quotes to avoid any special characters.