@classmethod
def _get_default_projection(cls):
    """Construct the default projection document."""
    projected = []
    neutral = []
    omitted = False
    for name, field in cls.__fields__.items():
        if field.project is None:
            neutral.append(name)
        elif field.project:
            projected.append(name)
        else:
            omitted = True
    if not projected and not omitted:
        return None
    elif not projected and omitted:
        projected = neutral
    return {field: (True) for field in projected}
