[Grails]NullPointerException sometimes occurs after upgrading the grails to the version 1.0.4

References

• bug information
  http://jira.codehaus.org/browse/GRAILS-3493
• Content Negotiation
  http://www.ibm.com/developerworks/java/library/j-grails09168/?S_TACT=105AGX90&S_CMP=EDU
  

Description

• Following exception sometimes occurs after upgrading the grails to the version 1.0.4.
  After starting up the grails jetty server, following exception occurs when accessing the application url. This exception occurs before executing the controller's beforeInterceptor() and any action method, this error is outputted by the grails HttpHeader parser program.
  

  java.lang.NullPointerException: Cannot invoke method toBigDecimal() on null object
       at org.codehaus.groovy.runtime.NullObject.invokeMethod(NullObject.java:77)
       at org.codehaus.groovy.runtime.InvokerHelper.invokePogoMethod(InvokerHelper.java:784)
       at org.codehaus.groovy.runtime.InvokerHelper.invokeMethod(InvokerHelper.java:758)
       at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodN(ScriptBytecodeAdapter.java:170)
       at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethod0(ScriptBytecodeAdapter.java:198)
       at org.codehaus.groovy.grails.web.mime.QualityComparator.compare(DefaultAcceptHeaderParser.groovy:122)
       at java.util.Arrays.mergeSort(Arrays.java:1284)
       at java.util.Arrays.sort(Arrays.java:1223)
       at java.util.Collections.sort(Collections.java:159)
       at org.codehaus.groovy.runtime.DefaultGroovyMethods.sort(DefaultGroovyMethods.java:3509)
       at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
       at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
       at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
       at java.lang.reflect.Method.invoke(Method.java:585)
       at org.codehaus.groovy.runtime.metaclass.ReflectionMetaMethod.invoke(ReflectionMetaMethod.java:51)
       at org.codehaus.groovy.runtime.metaclass.NewInstanceMetaMethod.invoke(NewInstanceMetaMethod.java:54)
       .......
  

Cause

• This problem is caused by the Http Content Negotiation logic and the values of http headers. If the user accesses the url, the browser is sending the http headers and values of the client information as follows
  (This output is sample http headers)
  

     accept: text/html,application/xhtml+xml,application/xml;q=0.9,/;q=0.8
   accept-language: en-us,en;q=0.5
   accept-encoding: gzip,deflate
   accept-charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
   keep-alive: 300
   connection: keep-alive
  

  Grails reads these http headers before executing the controller action, and DefaultAcceptHeaderParser program parses the http headers sent from the client. When the value of "accept" or "content type" http header is including the value "application/xhtml+xml" or "application/xml", Grails parses these http headers and tries to find the "q" parameter into the "accept" or "content-type" header.
  While parsing the headers, the NullPointerException occurs because some client program doesn't have the "q" parameter value into the http header even though the accept header includes the value "application/xhtml+xml" or "application/xml".

Resolution

• According to the http://jira.codehaus.org/browse/GRAILS-3493, this problem is fixed in grails 1.1.beta1. I tried to the grails 1.1.beta3, this problem is fixed.(but other error occurs.)