Cannot add comment to failed build

Expression buildNumber is undefined on line 10, column 29 in fragments/comment/commentFragment.ftl. 
The problematic instruction:  ${buildNumber} [on line 10, column 27 in fragments/comment/commentFragment.ftl] in user-directive ww.url [on line 6, column 5 in fragments/comment/commentFragment.ftl] 
Java backtrace for programmers:
freemarker.core.InvalidReferenceException: Expression buildNumber is undefined on line 10, column 29 in fragments/comment/commentFragment.ftl. 
at freemarker.core.TemplateObject.assertNonNull(TemplateObject.java:124) at freemarker.core.Expression.getStringValue(Expression.java:118) 
at freemarker.core.Expression.getStringValue(Expression.java:93) at freemarker.core.DollarVariable.accept(DollarVariable.java:76) 
at freemarker.core.Environment.visit(Environment.java:196) at freemarker.core.MixedContent.accept(MixedContent.java:92) at freemarker.core.Environment.visit(Environment.java:196) 
at freemarker.core.Environment.renderElementToString(Environment.java:1464) at freemarker.core.StringLiteral.getStringValue(StringLiteral.java:95) 
at freemarker.core.StringLiteral._getAsTemplateModel(StringLiteral.java:80) at freemarker.core.Expression.getAsTemplateModel(Expression.java:89) 
at freemarker.core.UnifiedCall.accept(UnifiedCall.java:110) at freemarker.core.Environment.visit(Environment.java:196) at freemarker.core.MixedContent.accept(MixedContent.java:92) 
at freemarker.core.Environment.visit(Environment.java:196) at freemarker.core.Environment.process(Environment.java:176) at freemarker.template.Template.process(Template.java:232) 
at com.opensymphony.webwork.views.freemarker.FreemarkerResult.doExecute(FreemarkerResult.java:153) 
at com.opensymphony.webwork.dispatcher.WebWorkResultSupport.execute(WebWorkResultSupport.java:143) 
at com.opensymphony.xwork.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:313) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:208) 
at com.opensymphony.xwork.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:115) 
at com.atlassian.bamboo.ww2.interceptors.BambooValidationInterceptor.doIntercept(BambooValidationInterceptor.java:33) 
at com.opensymphony.xwork.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:86) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:190) 
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:31) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:190) 

.... continuation.... 
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:31) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:190) 
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:31) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:190) 
at com.opensymphony.webwork.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:174) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:190) 
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:31) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:190) 
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:31) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:190) 
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:31) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:190) 
at com.opensymphony.xwork.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:151) 
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:190) 
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:31)