The following exception is thrown when upload is clicked without specifying a file. It should only be a frontend error and Confluence shouldn't attempt to upload the file.

006-04-21 16:58:06,466 ERROR [confluence.spaces.actions.AbstractLogoAction] doUpload Could not locate uploaded logo in request. Double check the file you are sending through.
com.atlassian.confluence.util.FileUploadUtils$FileUploadException
at com.atlassian.confluence.util.FileUploadUtils.handleFileUpload(FileUploadUtils.java:74)
at com.atlassian.confluence.spaces.actions.AbstractLogoAction.doUpload(AbstractLogoAction.java:59)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at com.opensymphony.