Config objects should be instanced without required config parameter

[bashleigh]

Issue type:

• question
• bug report
• feature request
• documentation issue

nestjs-config version

2.0.0-beta

@nestjs/common+core or other package versions

• @nestjs/common:
• @nestjs/core:

Excepted behavior

Actual behavior or outcome (for issue)

Replication/Example

    constructor(config) {
        Object.keys(config).forEach(key => this[key] = config[key]);
    }

Exception occurs when not passing to the constructor of extended types