fix 'Could not initialize class com.atlassian.plugins.conversion.convert.image.ImagingConverter'

[Myles Holloway]

Good afternoon, 

Situation

• I am are currently running Atlassian Confluence Server v 7.17
• I have recently completed an update from an older version (6.14)
• From the person that performed the upgrade in order to get it up and running after the upgrade they had to insert the pervious server.xml settings (they did NOT copy this file, just the custom changes alone)

System Info

Problem

• We are noticing that we cannot open or view attachments (images will show previews, but will not display in modal. PDFs and other forms of attachments are replaced with error message)
  • Console error when attempting to click an image to show as modal:

• 
  
  • The Following is the error shown in logs for the same occurrence
  • 2022-04-19 15:40:18,159 ERROR [https-jsse-nio2-8444-exec-20] [common.error.jersey.ThrowableExceptionMapper] toResponse Uncaught exception thrown by REST service: Could not initialize class com.atlassian.plugins.conversion.convert.image.ImagingConverter
    -- referer: https://[REDACTED]/display/EAMD/Upgrading+Atlassian+Suite | url: /rest/files/1.0/files/content/60391531/byAttachmentIds | traceId: aeeb8e2b1b7722ea | userName: [REDACTED]
    java.lang.NoClassDefFoundError: Could not initialize class com.atlassian.plugins.conversion.convert.image.ImagingConverter
    at com.atlassian.confluence.plugins.conversion.impl.DefaultConversionManager.getConverters(DefaultConversionManager.java:125)
    at com.atlassian.confluence.plugins.conversion.impl.DefaultConversionManager.isConvertible(DefaultConversionManager.java:109)
    at jdk.internal.reflect.GeneratedMethodAccessor1576.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.base/java.lang.reflect.Method.invoke(Unknown Source)
• When there is a PDF present on a page:
• 

Steps Taken

• Steps that have been outlined here and here, and have also cleared the system cache folders.
• However, to no avail, I can not resolve this issue.

Please, would someone help to resolve this.