plumbum patch to fix TEE with a stderr redirect

gistfile1.diff

diff --git a/plumbum/commands/modifiers.py b/plumbum/commands/modifiers.py
index 30f8dbf..1a5f8e6 100644
--- a/plumbum/commands/modifiers.py
+++ b/plumbum/commands/modifiers.py
@@ -151,12 +151,26 @@ class TEE(ExecutionModifier):
         with cmd.bgrun(retcode=self.retcode, stdin=None, stdout=PIPE, stderr=PIPE) as p:
             outbuf = []
             errbuf = []
+            buffers = {}
+            tee_to = {}
+
             out = p.stdout
             err = p.stderr
-            buffers = {out: outbuf, err: errbuf}
-            tee_to = {out: sys.stdout, err: sys.stderr}
+            read_from = []
+            if out:
+                buffers[out] = outbuf
+                tee_to[out] = sys.stdout
+                read_from.append(out)
+            if err:
+                buffers[err] = errbuf
+                tee_to[err] = sys.stderr
+                read_from.append(err)
+
+            if not read_from:
+                raise IOError("Can't TEE a process with no stdout or stderr")
+
             while p.poll() is None:
-                ready, _, _ = select((out, err), (), ())
+                ready, _, _ = select(read_from, (), ())
                 for fd in ready:
                     buf = buffers[fd]
                     data = os.read(fd.fileno(), 4096)