Fixed type error in apply-decorators.ts

[nikelborm]

PR Checklist

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• 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)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

Throws typescript error

Argument of type 'string | symbol | undefined' is not assignable to parameter of type 'string | symbol'.
  Type 'undefined' is not assignable to type 'string | symbol'

Here:

Because typescript definitions of Decorator types are as follows:

declare type ClassDecorator = <TFunction extends Function>(target: TFunction) => TFunction | void;
declare type PropertyDecorator = (target: Object, propertyKey: string | symbol) => void;
declare type MethodDecorator = <T>(target: Object, propertyKey: string | symbol, descriptor: TypedPropertyDescriptor<T>) => TypedPropertyDescriptor<T> | void;
declare type ParameterDecorator = (target: Object, propertyKey: string | symbol | undefined, parameterIndex: number) => void;

What is the new behavior?

Doesn't throw an error

Does this PR introduce a breaking change?

• Yes
• No

[nikelborm]

Apply-decorators were introduced here #3113