def issues_to_corpus(issues):
    """Convert from list of issues to a corpus.
    An issue will be extracted as its title, description and attachments.
    [title, descriptions, attachments]
    Note: Attachments is also a list of attachments' descriptions
    
    Parameters
    ----------
    issues: List of Issue object
        
    Returns
    -------
    corpus : A dictionary of extracted issues content.
    the key is issue's id and the values are a list of associated contents
    e.g, corpus = {12345:['issue title', 'issue descriptions', 
    ['attachment description 1', attachments description 2']]}
    """    
    corpus = {}
    for issue in issues:
        _id = issue.get_id()
        attachments = ' '.join(item for item in issue.get_attachments())
        content = [item for item in [issue.get_title(), issue.get_description(), attachments] if item != '' and item != None]
        corpus[_id] = content
    
    return corpus