What does this error mean?

[shahidkarimi]

from scrapy.core.engine import ExecutionEngine File "/usr/local/lib/python2.7/site-packages/scrapy/core/engine.py", line 14, in <module> from scrapy.core.downloader import Downloader File "/usr/local/lib/python2.7/site-packages/scrapy/core/downloader/__init__.py", line 16, in <module> from .middleware import DownloaderMiddlewareManager File "/usr/local/lib/python2.7/site-packages/scrapy/core/downloader/middleware.py", line 7, in <module> from scrapy.http import Request, Response File "/usr/local/lib/python2.7/site-packages/scrapy/http/__init__.py", line 11, in <module> from scrapy.http.request.form import FormRequest File "/usr/local/lib/python2.7/site-packages/scrapy/http/request/form.py", line 9, in <module> import lxml.html File "/usr/local/lib/python2.7/site-packages/lxml-3.4.4-py2.7-linux-x86_64.egg/lxml/html/__init__.py", line 42, in <module> from lxml import etree File "lxml.etree.pyx", line 161, in init lxml.etree (src/lxml/lxml.etree.c:198847) TypeError: encode() argument 1 must be string without null bytes, not unicode root@ip-104-238-95-53 [/home/karimi/www/scrapy_test]# scrapy --upgrade Traceback (most recent call last): File "/usr/local/bin/scrapy", line 3, in <module> from scrapy.cmdline import execute File "/usr/local/lib/python2.7/site-packages/scrapy/cmdline.py", line 7, in <module> from scrapy.crawler import CrawlerProcess File "/usr/local/lib/python2.7/site-packages/scrapy/crawler.py", line 5, in <module> from scrapy.core.engine import ExecutionEngine File "/usr/local/lib/python2.7/site-packages/scrapy/core/engine.py", line 14, in <module> from scrapy.core.downloader import Downloader File "/usr/local/lib/python2.7/site-packages/scrapy/core/downloader/__init__.py", line 16, in <module> from .middleware import DownloaderMiddlewareManager File "/usr/local/lib/python2.7/site-packages/scrapy/core/downloader/middleware.py", line 7, in <module> from scrapy.http import Request, Response File "/usr/local/lib/python2.7/site-packages/scrapy/http/__init__.py", line 11, in <module> from scrapy.http.request.form import FormRequest File "/usr/local/lib/python2.7/site-packages/scrapy/http/request/form.py", line 9, in <module> import lxml.html File "/usr/local/lib/python2.7/site-packages/lxml-3.4.4-py2.7-linux-x86_64.egg/lxml/html/__init__.py", line 42, in <module> from lxml import etree File "lxml.etree.pyx", line 161, in init lxml.etree (src/lxml/lxml.etree.c:198847) TypeError: encode() argument 1 must be string without null bytes, not unicode