Arguments that have custom parsers throw missing argument errors when the parsed value is falsy

[gkovalechyn]

In my project I have a simple command to delete an element by its index, but when the argument is "0" and is parsed to a number through a custom parser the validator fails due to a missing argument exception.

Example:

import { Command } from "@oclif/command";

export default class TestCommand extends Command {
	static description = "Throws a missing argument exception when the argument is 0";

	static args = [
		{
			name: "value",
			required: true,
			description: "A number",
			parse: (value: string): number => parseInt(value, 10)
		}
	];

	public async run(): Promise<void> {
		const { args } = this.parse(TestCommand);

		this.log(`Received: ${args.value}`);
	}
}

Running the command with the argument "0" it will throw an exception with saying it has a missing value even though it was provided while running it with the argument "1" will run the command successfuly.

It seems to be caused by this comparison:

parser/src/validate.ts

Line 37 in ac66076

if (!parse.output.argv[index]) {

[RasPhilCo]

Good catch!