function camelCase(subject) {
    var subjectString = coerceToString(subject);

    if (subjectString === '') {
      return '';
    }

    return words(subjectString)
      .map(wordToCamel)
      .join('');
  }
Converts the `subject` to <a href="https://en.wikipedia.org/wiki/CamelCase">camel case</a>.

@function camelCase
@static
@since 1.0.0
@memberOf Case
@param  {string} [subject=''] The string to convert to camel case.
@return {string}              The camel case string.
@example
v.camelCase('bird flight');
// => 'birdFlight'

v.camelCase('BirdFlight');
// => 'birdFlight'

v.camelCase('-BIRD-FLIGHT-');
// => 'birdFlight'