clean up null/undefined usages add missing cli.ext()
clean up null/undefined usages
add missing cli.ext()

kangax/html-minifier,kangax/html-minifier,AshKyd/html-minifier,kangax/html-lint,kangax/html-lint,DChristiany/html-minifier,AshKyd/html-minifier,DChristiany/html-minifier