问题：

在 appium v1.7.1 下，设置 desired_caps['automationName']='UIAutomator2'，在被测 app 输入账号和密码登录，输入账号和输入密码调用的方法相同，但是能正常输入账号，输入密码则报错：selenium.common.exceptions.WebDriverException: Message: An unknown server-side error occurred while processing the command. Original error: java.lang.NullPointerException。
在 appium v1.4.16 下同样设置 desired_caps['automationName']='UIAutomator2'，运行脚本则不会报错

环境：

Python3+Windows7+appium v1.7.1

测试代码：

self.login.inputName('test_apple')
self.login.inputPwd('asdf')

被调用的函数：

def inputName(self, username):
    self.clearTextEdit('com.duowan.makefriends:id/a9b')
    self.sendText('com.duowan.makefriends:id/a9b', username)

def inputPwd(self, pwd):
    self.clearTextEdit('com.duowan.makefriends:id/a9e')
    self.sendText('com.duowan.makefriends:id/a9e', pwd)

def sendText(self, elementInfo, text):
    self.findElement(elementInfo).send_keys(text)

def clearTextEdit(self, elementInfo):
    self.findElement(elementInfo).clear()

appium 报错

[MJSONWP] Encountered internal error running command:  {"jsonwp":{"value":"java.lang.NullPointerException\n\tat android.support.test.uiautomator.UiObject2.setText(UiObject2.java:601)\n\tat io.appium.uiautomator2.model.UiObject2Element.setText(UiObject2Element.java:129)\n\tat io.appium.uiautomator2.handler.SendKeysToElement.safeHandle(SendKeysToElement.java:83)\n\tat io.appium.uiautomator2.handler.request.SafeRequestHandler.handle(SafeRequestHandler.java:56)\n\tat io.appium.uiautomator2.server.AppiumServlet.handleRequest(AppiumServlet.java:202)\n\tat io.appium.uiautomator2.server.AppiumServlet.handleHttpRequest(AppiumServlet.java:193)\n\tat io.appium.uiautomator2.http.ServerHandler.channelRead(ServerHandler.java:44)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)\n\tat io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:345)\n\tat io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)\n\tat io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:345)\n\tat io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:435)\n\tat io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:293)\n\tat io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:267)\n\tat io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:250)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)\n\tat io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:345)\n\tat io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1294)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)\n\tat io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:911)\n\tat io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:131)\n\tat io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:611)\n\tat io.netty.channel.nio.NioEventLoop.processSelectedKeysPlain(NioEventLoop.java:514)\n\tat io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:468)\n\tat io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:438)\n\tat io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:140)\n\tat io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:144)\n\tat java.lang.Thread.run(Thread.java:841)\n","status":13,"sessionId":"aa2762e2-f14a-4e50-ad57-eb6d2e0b82df"}} ProxyRequestError: Could not proxy command to remote server. Original error: 500 - {"value":"java.lang.NullPointerException\n\tat android.support.test.uiautomator.UiObject2.setText(UiObject2.java:601)\n\tat io.appium.uiautomator2.model.UiObject2Element.setText(UiObject2Element.java:129)\n\tat io.appium.uiautomator2.handler.SendKeysToElement.safeHandle(SendKeysToElement.java:83)\n\tat io.appium.uiautomator2.handler.request.SafeRequestHandler.handle(SafeRequestHandler.java:56)\n\tat io.appium.uiautomator2.server.AppiumServlet.handleRequest(AppiumServlet.java:202)\n\tat io.appium.uiautomator2.server.AppiumServlet.handleHttpRequest(AppiumServlet.java:193)\n\tat io.appium.uiautomator2.http.ServerHandler.channelRead(ServerHandler.java:44)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)\n\tat io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:345)\n\tat io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)\n\tat io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:345)\n\tat io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:435)\n\tat io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:293)\n\tat io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:267)\n\tat io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:250)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)\n\tat io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:345)\n\tat io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1294)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)\n\tat io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)\n\tat io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:911)\n\tat io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:131)\n\tat io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:611)\n\tat io.netty.channel.nio.NioEventLoop.processSelectedKeysPlain(NioEventLoop.java:514)\n\tat io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:468)\n\tat io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:438)\n\tat io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:140)\n\tat io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:144)\n\tat java.lang.Thread.run(Thread.java:841)\n","status":13,"sessionId":"aa2762e2-f14a-4e50-ad57-eb6d2e0b82df"}
    at JWProxy.proxy$ (C:\Users\wen\AppData\Local\Programs\appium-desktop\resources\app\node_modules\appium\node_modules\appium-base-driver\lib\jsonwp-proxy\proxy.js:152:13)
    at tryCatch (C:\Users\wen\AppData\Local\Programs\appium-desktop\resources\app\node_modules\appium\node_modules\babel-runtime\regenerator\runtime.js:67:40)
    at GeneratorFunctionPrototype.invoke [as _invoke] (C:\Users\wen\AppData\Local\Programs\appium-desktop\resources\app\node_modules\appium\node_modules\babel-runtime\regenerator\runtime.js:315:22)
    at GeneratorFunctionPrototype.prototype.(anonymous function) [as throw] (C:\Users\wen\AppData\Local\Programs\appium-desktop\resources\app\node_modules\appium\node_modules\babel-runtime\regenerator\runtime.js:100:21)
    at GeneratorFunctionPrototype.invoke (C:\Users\wen\AppData\Local\Programs\appium-desktop\resources\app\node_modules\appium\node_modules\babel-runtime\regenerator\runtime.js:136:37)

代码报错：

selenium.common.exceptions.WebDriverException: Message: An unknown server-side error occurred while processing the command. Original error: java.lang.NullPointerException
    at android.support.test.uiautomator.UiObject2.setText(UiObject2.java:601)
    at io.appium.uiautomator2.model.UiObject2Element.setText(UiObject2Element.java:129)
    at io.appium.uiautomator2.handler.SendKeysToElement.safeHandle(SendKeysToElement.java:83)
    at io.appium.uiautomator2.handler.request.SafeRequestHandler.handle(SafeRequestHandler.java:56)
    at io.appium.uiautomator2.server.AppiumServlet.handleRequest(AppiumServlet.java:202)
    at io.appium.uiautomator2.server.AppiumServlet.handleHttpRequest(AppiumServlet.java:193)
    at io.appium.uiautomator2.http.ServerHandler.channelRead(ServerHandler.java:44)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:345)
    at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:102)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:345)
    at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:435)
    at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:293)
    at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:267)
    at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:250)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:345)
    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1294)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:366)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:352)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:911)
    at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:131)
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:611)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysPlain(NioEventLoop.java:514)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:468)
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:438)
    at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:140)
    at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:144)
    at java.lang.Thread.run(Thread.java:841)