src/vs/workbench/services/configurationResolver/common/variableResolver.ts/AbstractVariableResolverService/resolveFromMap
class AbstractVariableResolverService:	private resolveFromMap(variableKind: VariableKind, match: string, argument: string | undefined, commandValueMapping: IStringDictionary<string> | undefined, prefix: string | undefined): string {
		if (argument && commandValueMapping) {
			const v = (prefix === undefined) ? commandValueMapping[argument] : commandValueMapping[prefix + ':' + argument];
			if (typeof v === 'string') {
				return v;
			}
			throw new VariableError(variableKind, localize('noValueForCommand', "Variable {0} can not be resolved because the command has no value.", match));
		}
		return match;
	}