我有 spring mvc 项目，我上传 xml 文件并尝试通过 DOM 将其写入我的 xml，但遇到了这个异常。当我尝试在平常的项目中执行相同的过程时 - 一切正常。无法理解为什么会发生..
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:894)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:789)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
root cause
java.lang.NullPointerException
org.apache.xml.utils.TreeWalker.dispatachChars(TreeWalker.java:303)
org.apache.xml.utils.TreeWalker.startNode(TreeWalker.java:447)
org.apache.xml.utils.TreeWalker.traverse(TreeWalker.java:202)
org.apache.xalan.transformer.TransformerIdentityImpl.transform(TransformerIdentityImpl.java:343)
com.mycompany.xmlloader.xmlHandler.DOMParser.saveToCatalog(DOMParser.java:147)
com.mycompany.xmlloader.service.XMLServiceImpl.updateCatalog(XMLServiceImpl.java:48)
com.mycompany.xmlloader.controller.XMLController.uploadToCatalog(XMLController.java:47)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:601)
org.springframework.web.method.support.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:213)
org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:126)
org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:96)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617)
org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578)
org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:789)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
和代码片段：
TransformerFactory transfac = TransformerFactory.newInstance();
Transformer trans = …