Don't scatter explicit undefineds through objects because of unused rules

example.js

@@ -5,7 +5,8 @@ const { validateValue } = require("@validatem/core");
 const isString = require("@validatem/is-string");
 
 let validator = hasShape({
-	foo: [ isString ]
+	foo: [ isString ],
+	unused: [ isString ]
 });
 
 let objectA = {

index.js

@@ -75,7 +75,11 @@ module.exports = function hasShape(rules) {
 					});
 
 					errors.push(... annotatedErrors);
-					newObject[key] = newValue;
+
+					// Don't scatter explicit `undefined`s across the result object, just because an optional rule existed for some properties but the corresponding value didn't
+					if (newValue !== undefined) {
+						newObject[key] = newValue;
+					}
 				} else {
 					// Extraneous property
 					newObject[key] = value;