Error evaluating expression: Cannot invoke method getAt() on null object

Question

I have a Question domain model designed as follows

class Question {

    List<Choice> choiceCollection;

    static hasMany = [choiceCollection:Choice]
    static mappping = {
        choiceCollection(joinTable:false)
    }

}

To fulfill my needs, /grails-app/views/question/create.gsp has been customized as you can see below

create.gsp

<g:each var="i" in="${(0..4)}">
    <div class="fieldcontain  required">
    <label for="description">
            Option ${i + 1}.
            <span class="required-indicator">*</span>
        </label>
        <g:textArea name="choiceCollection[${i}].description" cols="40" rows="5" maxlength="2000" value="${questionInstance?.choiceCollection[i]?.description}"/>
    </div>
</g:each>

When i try to access create view, i get the following error

Error evaluating expression [questionInstance?.choiceCollection[i]?.description]: Cannot invoke method getAt() on null object

Question: What should i do to run my application ?

Grails version: 2.1.1

Solution 1

Instead of accessing by [] use getAt, then the ? Operator will work:

choiceCollection?.getAt(1)?.description

Solution 2

I observed this error when attempting to run grails (2.2.4) using Java 8. The cause was not immediately obvious. It's buried somewhere grails.util.BuildSettings.groovy

When I reverted to java 1.7, the message went away.

Comments

[Arthur Ronald]

Nice one (+1). Just for curiosity: why getAt method whether List API does not define one ???

[Chris]

Thx. Regarding your question:There is one in the java.util.List of groovy: groovy.codehaus.org/groovy-jdk/java/util/List.html

[Korobko Alex]

Can I just use get instead of getAt?

[Chris]

Unfortunately not always, but possibly in this specific case