[3.8] Fix NPE when importing newspaper course with metadata

[matthias-ronge]

Backported #6390 to 3.8.x branch

[henning-gerhardt]

Short note: This changes are difficult to review as there are no tests added nor I have some example data to test this changes with, so I need more time for reviewing this.

[henning-gerhardt]

A team mate created a small newspaper course xml file for me which contains some meta data:

<?xml version="1.0" encoding="UTF-8"?>
<course>
   <description>Die Zeitung erschien vom 1. Februar 1757 bis zum 07. Februar 1757 regelmäßig an allen Montagen und Mittwochen.</description>
   <processes>
      <process>
         <title index="1">
            <appeared date="1757-02-02">
               <metadata metadataType="slub_script" value="Fraktur"/>
               <metadata metadataType="LegalNoteAndTermsOfUse" value="PDM1.0"/>
               <metadata metadataType="DocLanguage" value="ger"/>
               <metadata metadataType="slub_ownerDigi" value="SLUB Dresden"/>
            </appeared>
         </title>
      </process>
      <process>
         <title index="1">
            <appeared date="1757-02-07"/>
         </title>
      </process>
   </processes>
</course>

After uploading this file I got the following stack trace

java.lang.ClassCastException: class org.kitodo.production.forms.createprocess.ProcessSelectMetadata cannot be cast to class org.kitodo.production.forms.createprocess.ProcessTextMetadata (org.kitodo.production.forms.createprocess.ProcessSelectMetadata and org.kitodo.production.forms.createprocess.ProcessTextMetadata are in unnamed module of loader org.apache.catalina.loader.ParallelWebappClassLoader @1b6eb4d)
	at org.kitodo.production.model.bibliography.course.metadata.CountableMetadata.setStartValue(CountableMetadata.java:305)
	at org.kitodo.production.model.bibliography.course.Course.processRecoveredMetadata(Course.java:396)
	at org.kitodo.production.model.bibliography.course.Course.<init>(Course.java:315)
	at org.kitodo.production.forms.CalendarForm.upload(CalendarForm.java:625)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at org.apache.el.parser.AstValue.invoke(AstValue.java:252)
	at org.apache.el.MethodExpressionImpl.invoke(MethodExpressionImpl.java:266)
	....

While reading the code I found in the new introduced code a potential null pointer exception which I only see after the test execution was minimal adjusted (second parameter was set to null). I will comment this in the code change.

[henning-gerhardt]

Potential null pointer exception if possibleProcessDetails ist set to null like in the test execution (see CourseTest.java line 34). The test code execution did not cover this peace of code.