A minor simplification.
Add missing quotes.

Without the quotes, trying to print the value of an expression that
was entered by the user (with the default mapping of "<Leader>v/")
would cause an error like this:

    === 18472 === !!! At least one child process is still running when POE::Kernel->run() is ready to return.
    === 18472 === !!! Be sure to use sig_child() to reap child processes.
    === 18472 === !!! In extreme cases, failure to reap child processes has
    === 18472 === !!! resulted in a slow 'fork bomb' that has halted systems.

    ERROR 002.  Please email vimdebug at iijo dot org.