maybeCoerceNumber bombs if coerce produced an object without toString

I ran into this trying to use pg-connection-string.parse as a coerce function today, it returns an object with a null prototype which can't be coerced to a string.

import yargs from 'yargs';
import {parse as pgcs_parse} from 'pg-connection-string';


const parser = yargs('--db=postgresql://db/something'.split(/\s+/))
  .strict()
  .option('db', {
    coerce: pgcs_parse,
  })
  .fail((_, err) => {
    console.error(err.stack);
    process.exit(1);
  })
  ;

const argv = parser.parse();

console.log(argv);

:; ts-node test.ts
YError: Cannot convert object to primitive value
    at Object.parseArgs [as _parseArgs] (.../node_modules/yargs/build/index.cjs:2762:27)
    at Object.parse (.../node_modules/yargs/build/index.cjs:2260:31)
    at Object.<anonymous> (.../test.ts:16:21)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Module.m._compile (/usr/local/lib/node_modules/ts-node/src/index.ts:858:23)
    at Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Object.require.extensions.<computed> [as .ts] (/usr/local/lib/node_modules/ts-node/src/index.ts:861:12)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)

The original stack trace is lost when it gets converted to YError, but the problem occurs in looksLikeNumber when the regexp is applied. It seems to me that maybeCoerceNumber could check if value is a string before doing anything more.

Start by locating maybeCoerceNumber and the looksLikeNumber call described in the issue, then reproduce the supplied pg-connection-string example. Check the available parser tests or test suite and confirm the example no longer raises the reported conversion error while normal number handling remains intact.