When I open a project, the default /issues page is shown. However, I don't see any issues in it. It's looks as if there are no issues in the project. The browser console gives this error:

And the log file gives this stack trace:
2018-08-20 15:42:28,472 http-nio-8080-exec-47 ERROR [o.a.c.c.C.[.[localhost].[/jira].[default]] Servlet.service() for servlet [default] in context with path [/jira] threw exception
org.codehaus.jackson.map.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: com.atlassian.jira.plugin.issuenav.service.issuetable.IssueTableServiceOutcome["issueTable"]->com.atlassian.jira.plugin.issuenav.service.issuetable.IssueTable["table"]->com.google.common.collect.TransformingRandomAccessList[9])
at org.codehaus.jackson.map.JsonMappingException.wrapWithPath(JsonMappingException.java:218)
at org.codehaus.jackson.map.JsonMappingException.wrapWithPath(JsonMappingException.java:197)
at org.codehaus.jackson.map.ser.std.SerializerBase.wrapAndThrow(SerializerBase.java:166)
at org.codehaus.jackson.map.ser.std.StdContainerSerializers$IndexedListSerializer.serializeContents(StdContainerSerializers.java:127)
at org.codehaus.jackson.map.ser.std.StdContainerSerializers$IndexedListSerializer.serializeContents(StdContainerSerializers.java:71)
at org.codehaus.jackson.map.ser.std.AsArraySerializerBase.serialize(AsArraySerializerBase.java:86)
at org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:446)
at org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:150)
at org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
at org.codehaus.jackson.map.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:446)
at org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:150)
at org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
at org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:610)
at org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:256)
at org.codehaus.jackson.map.ObjectMapper.writeValue(ObjectMapper.java:1604)
at org.codehaus.jackson.jaxrs.JacksonJsonProvider.writeTo(JacksonJsonProvider.java:558)
at com.sun.jersey.spi.container.ContainerResponse.write(ContainerResponse.java:302)
... 5 filtered
at com.atlassian.plugins.rest.module.RestDelegatingServletFilter$JerseyOsgiServletContainer.doFilter(RestDelegatingServletFilter.java:154)
... 1 filtered
at com.atlassian.plugins.rest.module.RestDelegatingServletFilter.doFilter(RestDelegatingServletFilter.java:68)
... 90 filtered
at com.atlassian.jira.security.JiraSecurityFilter.doFilter(JiraSecurityFilter.java:70)
... 16 filtered
at com.atlassian.plugins.rest.module.servlet.RestSeraphFilter.doFilter(RestSeraphFilter.java:37)
... 73 filtered
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at com.atlassian.jira.plugin.issuenav.service.issuetable.SplitViewIssueTableCreator$1.apply(SplitViewIssueTableCreator.java:45)
at com.atlassian.jira.plugin.issuenav.service.issuetable.SplitViewIssueTableCreator$1.apply(SplitViewIssueTableCreator.java:34)
at com.google.common.collect.Lists$TransformingRandomAccessList.get(Lists.java:608)
at org.codehaus.jackson.map.ser.std.StdContainerSerializers$IndexedListSerializer.serializeContents(StdContainerSerializers.java:106)
Looks like some sort of null pointer exception.
Re-indexing JIRA didn't help. I can view the issues in the project if I use the search jql view, so I know they exist. I'm using on-premise JIRA version 7.1.9.
The integrity checker crashes in the workflows section, specifically regarding the "Check JIRA issues with null status" part. When I search for issues with "status = null", I get 2 subtasks from the project in question. Attempting to do anything with those subtasks from the search view results in an error: "There were errors loading the issue." Trying to change the workflow results in:
Any idea how I can resolve this? It looks like I need to fix or delete those two offending subtasks. Do I need to go into the database level to fix this?