我试图使用scrapy的项目管道在表中插入spider中的四个项目，除了doc_id项目中有空值（来自原始源，并使用regex清理）之外，一切都很顺利。
我这里的问题是，一旦它找到一个空值，整行将被丢弃，而当我将数据导出为csv文件时，如果有一个列中没有任何值，则完全可以。
下面是我得到的关键错误：

Traceback (most recent call last):
  File "/Users/opt/anaconda3/lib/python3.7/site-packages/twisted/internet/defer.py", line 654, in _runCallbacks
    current.result = callback(current.result, *args,**kw)
  File "/Users/opt/anaconda3/lib/python3.7/site-packages/scrapy/utils/defer.py", line 154, in f
    return deferred_from_coro(coro_f(*coro_args,**coro_kwargs))
  File "/Users/user/document_scraper/doc/pipelines.py", line 32, in process_item
    self.store_db(item)
  File "/Users/user/document_scraper/doc/pipelines.py", line 40, in store_db
    item['doc_id'][0],
  File "/Users/opt/anaconda3/lib/python3.7/site-packages/scrapy/item.py", line 83, in __getitem__
    return self._values[key]
KeyError: 'doc_id'

my items.py：

import scrapy
from scrapy.loader import ItemLoader
from itemloaders.processors import TakeFirst, MapCompose, Compose
import re
class DocItem(scrapy.Item):
    date = scrapy.Field()
    office = scrapy.Field(output_processor = TakeFirst())
    doc_body = scrapy.Field()
    doc_id = scrapy.Field(input_processor = MapCompose(lambda item: re.findall('C\.\s\d{4}', item)[0].split('C. ')[1]))

my pipelines.py：

import sqlite3
class DocPipeline(object):
    def __init__(self):
        self.create_connection()
        self.create_table()
    def create_connection(self):
        self.conn = sqlite3.connect("//document.db")
        self.curr = self.conn.cursor()
    def create_table(self):
        self.curr.execute("""DROP TABLE IF EXISTS DOC""")
        self.curr.execute("""CREATE TABLE DOC(
            DOC_DATE date,
            OFFICE text,
            BODY text,
            DOC_ID number
        )""")
    def process_item(self, item, spider):
        self.store_db(item)
        return item
    def store_db(self, item):
        self.curr.execute("""INSERT INTO DOC VALUES (?,?,?,?)""",(
            item['date'][0],
            item['office'],
            item['doc_body'][0],
            item['doc_id'][0],
        ))
        self.conn.commit()

我如何告诉sqlite或scrapy我希望返回我的项目，而不管其中一列中的值是“无”呢？