Stash not returning JIRA summary data when running JDK 1.6

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'branchDevSummary' defined in URL [bundle://73.0:0/META-INF/spring/atlassian-plugins-components.xml]: Unsatisfied dependency expressed through constructor argument with index 0 of type [com.atlassian.stash.internal.jira.index.JiraIndexService]: : Error loading class [com.atlassian.stash.internal.jira.summary.impl.CompositeDevSummaryService] for bean with name 'devSummaryService' defined in URL [bundle://73.0:0/META-INF/spring/atlassian-plugins-components.xml]: problem with class file or dependent class; nested exception is java.lang.UnsupportedClassVersionError: com/atlassian/stash/internal/jira/summary/InternalDevSummaryService : Unsupported major.minor version 51.0; nested exception is org.springframework.beans.factory.CannotLoadBeanClassException: Error loading class [com.atlassian.stash.internal.jira.summary.impl.CompositeDevSummaryService] for bean with name 'devSummaryService' defined in URL [bundle://73.0:0/META-INF/spring/atlassian-plugins-components.xml]: problem with class file or dependent class; nested exception is java.lang.UnsupportedClassVersionError: com/atlassian/stash/internal/jira/summary/InternalDevSummaryService : Unsupported major.minor version 51.0
	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:591) ~[spring-beans-4.0.2.RELEASE.jar:4.0.2.RELEASE]
	at java.security.AccessController.doPrivileged(Native Method) ~[na:1.6.0_45]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728) ~[spring-context-4.0.2.RELEASE.jar:4.0.2.RELEASE]
	at java.lang.Thread.run(Thread.java:662) [na:1.6.0_45]
	... 19 frames trimmed
Caused by: org.springframework.beans.factory.CannotLoadBeanClassException: Error loading class [com.atlassian.stash.internal.jira.summary.impl.CompositeDevSummaryService] for bean with name 'devSummaryService' defined in URL [bundle://73.0:0/META-INF/spring/atlassian-plugins-components.xml]: problem with class file or dependent class; nested exception is java.lang.UnsupportedClassVersionError: com/atlassian/stash/internal/jira/summary/InternalDevSummaryService : Unsupported major.minor version 51.0
	at org.springframework.beans.factory.support.AbstractBeanFactory.resolveBeanClass(AbstractBeanFactory.java:1144) ~[spring-beans-4.0.2.RELEASE.jar:4.0.2.RELEASE]
	... 4 common frames omitted
Caused by: java.lang.UnsupportedClassVersionError: com/atlassian/stash/internal/jira/summary/InternalDevSummaryService : Unsupported major.minor version 51.0
	at java.lang.ClassLoader.defineClass1(Native Method) ~[na:1.6.0_45]
	at org.springframework.util.ClassUtils.forName(ClassUtils.java:211) ~[spring-2.5.6.SEC02.jar:4.0.2.RELEASE]
	... 4 common frames omitted