<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def build_job(name=None, parameters=None):
    '''
    Initiate a build for the provided job.

    :param name: The name of the job is check if it exists.
    :param parameters: Parameters to send to the job.
    :return: True is successful, otherwise raise an exception.

    CLI Example:

    .. code-block:: bash

        salt '*' jenkins.build_job jobname

    '''
    if not name:
        raise SaltInvocationError('Required parameter \'name\' is missing')

    server = _connect()

    if not job_exists(name):
        raise CommandExecutionError('Job \'{0}\' does not exist.'.format(name))

    try:
        server.build_job(name, parameters)
    except jenkins.JenkinsException as err:
        raise CommandExecutionError(
            'Encountered error building job \'{0}\': {1}'.format(name, err)
        )
    return True