第一步我执行了install就报了这个错，怎么解决
Traceback (most recent call last):
File "setup.py", line 115, in <module>
if CheckDmHome(path):
File "setup.py", line 59, in CheckDmHome
write_pystr='import os\nos.add_dll_directory(r''+os.environ.get("DM_HOME")+'\bin'+'')'
TypeError: can only concatenate str (not "NoneType") to str

这个问题怎么解决