hang on chain if pipe nothing to awk

[RPing]

delegator.chain("printf '' | awk '{print $1}'") would hang, while
delegator.run("printf '' | awk '{print $1}'") wouldn't.
It seems that the command would block in pexpect：

^C---------------------------------------------------------------------------
KeyboardInterrupt                         Traceback (most recent call last)
<ipython-input-3-fc2320a6bab7> in <module>
----> 1 delegator.chain("printf '' | awk '{print $1}'")

~/.pyenv/versions/3.7.0/lib/python3.7/site-packages/delegator.py in chain(command, timeout, cwd, env)
    308             c.subprocess.sendeof()
    309
--> 310         data = c.out
    311
    312     return c

~/.pyenv/versions/3.7.0/lib/python3.7/site-packages/delegator.py in out(self)
    126             self.__out = self.std_out.read()
    127         else:
--> 128             self.__out = self._pexpect_out
    129
    130         return self.__out

~/.pyenv/versions/3.7.0/lib/python3.7/site-packages/delegator.py in _pexpect_out(self)
    114             result += self.subprocess.after
    115
--> 116         result += self.subprocess.read()
    117         return result
    118

~/.pyenv/versions/3.7.0/lib/python3.7/site-packages/pexpect/spawnbase.py in read(self, size)
    439         if size < 0:
    440             # delimiter default is EOF
--> 441             self.expect(self.delimiter)
    442             return self.before
    443

~/.pyenv/versions/3.7.0/lib/python3.7/site-packages/pexpect/spawnbase.py in expect(self, pattern, timeout, searchwindowsize, async_, **kw)
    339         compiled_pattern_list = self.compile_pattern_list(pattern)
    340         return self.expect_list(compiled_pattern_list,
--> 341                 timeout, searchwindowsize, async_)
    342
    343     def expect_list(self, pattern_list, timeout=-1, searchwindowsize=-1,

~/.pyenv/versions/3.7.0/lib/python3.7/site-packages/pexpect/spawnbase.py in expect_list(self, pattern_list, timeout, searchwindowsize, async_, **kw)
    367             return expect_async(exp, timeout)
    368         else:
--> 369             return exp.expect_loop(timeout)
    370
    371     def expect_exact(self, pattern_list, timeout=-1, searchwindowsize=-1,

~/.pyenv/versions/3.7.0/lib/python3.7/site-packages/pexpect/expect.py in expect_loop(self, timeout)
    111                 incoming = spawn.read_nonblocking(spawn.maxread, timeout)
    112                 if self.spawn.delayafterread is not None:
--> 113                     time.sleep(self.spawn.delayafterread)
    114                 if timeout is not None:
    115                     timeout = end_time - time.time()

KeyboardInterrupt:

My delegator version is 0.1.1