Exceptions in logs when custom field default user is deleted

2006-06-09 11:45:19,874 ERROR [issue.customfields.impl.AbstractSingleFieldType] Incorrect formatted custom field stored 
as default
com.atlassian.jira.issue.customfields.impl.FieldValidationException: User 'bob' was not found in the system
        at com.atlassian.jira.issue.customfields.converters.UserConverter.getUser(UserConverter.java:38)
        at com.atlassian.jira.issue.customfields.impl.UserCFType.getSingularObjectFromString(UserCFType.java:33)
        at com.atlassian.jira.issue.customfields.impl.StringCFType.getObjectFromDbValue(StringCFType.java:25)
        at com.atlassian.jira.issue.customfields.impl.AbstractSingleFieldType.getDefaultValue(AbstractSingleFieldType.ja
va:141)
        at com.atlassian.jira.plugin.customfield.CustomFieldTypeModuleDescriptor.getDefaultViewHtml(CustomFieldTypeModul
eDescriptor.java:136)
        at com.atlassian.jira.issue.customfields.config.item.DefaultValueConfigItem.getViewHtml(DefaultValueConfigItem.j
ava:21)
        at com.atlassian.jira.issue.fields.config.FieldConfigItemImpl.getViewHtml(FieldConfigItemImpl.java:24)
        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 webwork.util.InjectionUtils$DefaultInjectionImpl.invoke(InjectionUtils.java:61)
        at webwork.util.InjectionUtils.invoke(InjectionUtils.java:52)
        at webwork.util.ValueStack.findValue(ValueStack.java:426)
        at webwork.util.ValueStack.findValue(ValueStack.java:175)
        at webwork.view.taglib.WebWorkBodyTagSupport.findValue(WebWorkBodyTagSupport.java:61)
        at webwork.view.taglib.BasicPropertyTag.doStartTag(BasicPropertyTag.java:54)
        at org.apache.jsp.secure.admin.views.customfields.configurecustomfield_jsp._jspx_meth_webwork_property_16(org.ap
ache.jsp.secure.admin.views.customfields.configurecustomfield_jsp:1873)
        at org.apache.jsp.secure.admin.views.customfields.configurecustomfield_jsp._jspx_meth_webwork_iterator_2(org.apa
che.jsp.secure.admin.views.customfields.configurecustomfield_jsp:1488)
        at org.apache.jsp.secure.admin.views.customfields.configurecustomfield_jsp._jspx_meth_webwork_iterator_1(org.apa
che.jsp.secure.admin.views.customfields.configurecustomfield_jsp:1441)
        at org.apache.jsp.secure.admin.views.customfields.configurecustomfield_jsp._jspx_meth_webwork_if_2(org.apache.js
p.secure.admin.views.customfields.configurecustomfield_jsp:1404)
        at org.apache.jsp.secure.admin.views.customfields.configurecustomfield_jsp._jspService(org.apache.jsp.secure.adm
in.views.customfields.configurecustomfield_jsp:282)
        at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:97)
.....