Make metadata optional

[devlzcode]

Quality of life update for those who use @Module({}) and would rather @Module()

PR Checklist

Please check if your PR fulfills the following requirements:

• [ ] The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• [ ] Bugfix
• [ ] Feature
• [ ] Code style update (formatting, local variables)
• [x] Refactoring (no functional changes, no api changes)
• [ ] Build related changes
• [ ] CI related changes
• [ ] Other... Please describe:

What is the current behavior?

@Module() requires a parameter

Issue Number: N/A

What is the new behavior?

@Module() will default to {} if no parameters given

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 2ae643ea-1ff2-4210-bd92-b284859653ab

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.816%

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Totals
Change from base Build 524b0569-b11d-460d-a48f-9dcb01ffde7f:	0.0%
Covered Lines:	6099
Relevant Lines:	6501

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💛 - Coveralls