How to use SprintManagerImpl

Hello,

I want to gather a list of sprints using SprintManager and SprintManagerImpl.
This is what I have tried but it crashes.

public class GetSprintsForUI implements ValuesGenerator {


    @Override
    public Map getValues(Map map) {
            SprintManager spm = new SprintManagerImpl();
            Map<String, String> sprintsMap = new HashMap<String, String>();
            ServiceOutcome<Collection<Sprint>> serviceOutcome = spm.getAllSprints();
            if(serviceOutcome==null){
                return null;
            }
            for(Sprint s : serviceOutcome.getValue()){
                sprintsMap.put(String.valueOf(s.getId()),s.getName());
            }
            return sprintsMap;
    }
}

This is the error I get:

Caused by: java.lang.NullPointerException
	at com.atlassian.greenhopper.service.sprint.SprintManagerImpl.getAllSprints(SprintManagerImpl.java:123) [?:?]
	at com.jiraPlugin.utility.GetSprintsForUI.getValues(GetSprintsForUI.java:47) [?:?]
	at com.atlassian.configurable.ValuesGeneratorObjectConfigurationProperty.getInternalValues(ValuesGeneratorObjectConfigurationProperty.java:75) [classes/:?]
	at com.atlassian.configurable.ObjectConfigurationPropertyImpl.entrySet(ObjectConfigurationPropertyImpl.java:266) [classes/:?]
	at com.atlassian.jira.plugin.corereports.web.action.ConfigureReport.mapAndConvertToList(ConfigureReport.java:383) [?:?]
	at com.atlassian.jira.plugin.corereports.web.action.ConfigureReport.access$000(ConfigureReport.java:53) [?:?]
	at com.atlassian.jira.plugin.corereports.web.action.ConfigureReport$ObjectConfigurationField.getValues(ConfigureReport.java:440) [?:?]
	... 387 more

Does anyone knows what am I doing wrong?
Thank you.