GetBoolean = function (source, key, defaultValue)
{
    if (!source)
    {
        return defaultValue;
    }
    else if (source.hasOwnProperty(key))
    {
        return source[key];
    }
    else
    {
        return defaultValue;
    }
}
Retrieves the value of the given key from an object.

@function Phaser.Tweens.Builders.GetBoolean
@since 3.0.0

@param {object} source - The object to retrieve the value from.
@param {string} key - The key to look for in the `source` object.
@param {boolean} defaultValue - The default value to return if the `key` doesn't exist or if no `source` object is provided.

@return {boolean} The retrieved value.