Bug: fitting input as object with a key with the value 'false' - is lost - kept as `undefined`

[royrothman]

Consider this:

bagpipes:
   some-flow:
    - some-fitting:
         key: false

When I play the pipe - I get the false of the ctx.input as undefined 😢

bug reproduction:

const bagpipes = require('bagpipes');
const pipes = bagpipes.create({ 'foo' : [ { emit: { bar: false } } ] } );
pipes.play( pipes.getPipe( 'foo' ) , ctx = {} );

if( ctx.output.bar !== false) throw new Error('oups. expected false, but got something else');

Thanks