cd command with two arguments to do directory substitution

At some place I've worked in the past I had the ability to issue a CD command with two parameters. Extensive googling for this resulted in nothing, so I wrote this bash function to do it.

Using 'cd' in this mode will replace the first occurrence of the first parameter with the second parameter. The simplest use case is changing from classes to src directory when in a deep directory structure:

$ pwd
/home/rcs/project/src/com/xyz/custom/some/really/deep/path
$ cd src classes
$ pwd
/home/rcs/project/classes/com/xyz/custom/some/really/deep/path

function cd {
        if [ -z $2 ]
        then
                builtin cd $1
        else
                builtin cd `echo $PWD | sed s/$1/$2/`
        fi
}

It's not bullet proof, but it's decreased the achyness in my typing fingers!

EDIT - I found a few bugs with the function; namely I could not change dir to a directory that contained spaces. Once I made a change to correct this problem, I could no longer issue 'cd' to return to my home directory.

Here are my change to correct these problems:

function cd {
    if [ -z "$2" ]
    then
        if [ -z "$1" ]
        then
            builtin cd
        else
            builtin cd "$*"
        fi
    else
        builtin cd `echo $PWD | sed s/$1/$2/`
    fi
}