AttributeError: 'NoneType' object has no attribute 'encode' with lxml-python

问题

I'm getting AttributeError: 'NoneType' object has no attribute 'encode' error when parsing out some XML patent inventor data. I'm trying to pull the first inventor plus their address infomation into a string as such below:

inventor1 = first(doc.xpath('//applicants/applicant/addressbook/last-name/text()'))
inventor2 = first(doc.xpath('//applicants/applicant/addressbook/first-name/text()'))
inventor3 = first(doc.xpath('//applicants/applicant/addressbook/address/city/text()'))
inventor4 = first(doc.xpath('//applicants/applicant/addressbook/address/state/text()'))
inventor5 = first(doc.xpath('//applicants/applicant/addressbook/address/country/text()'))
inventor = str(inventor2.encode("UTF-8")) + " " + str(inventor1.encode("UTF-8"))
inventors2 = str(inventor3.encode("UTF-8")) + ", " + str(inventor4) + ", " + str(inventor5)
inventors = str(inventor) + ", " + str(inventors2)

print "DocID: {0}\nGrantDate: {1}\nApplicationDate: {2}\nNumber of Claims: {3}\nExaminers: {4}\nAssignee: {5}\nInventor: {6}\n".format(docID,grantdate,applicationdate,claimsNum,examiners.encode("UTF-8"),assignees,inventors)

but there is problem as there is a UnicodeEncodeError: 'ascii' codec can't encode character for multiple parts in this long xml. I need to have the .encodes within my python so I don't create an error but by doing so I get this:

Traceback (most recent call last):
  File "C:\Documents and Settings\Desktop\FINAL BART INFO ONE.py", line 87, in <module> inventor = str(inventor2.encode("UTF-8")) + " " + str(inventor1.encode("UTF-8"))
AttributeError: 'NoneType' object has no attribute 'encode'

Is there anyway to either ignore the "None" values that are returned when nothing is there? Must I def or use a different type of .encode for my print?

By the way i'm creating a database from an input file is actually multiple XML files appending to one file. (Data file Sourced from Google Patents).