You said that you are using a base 10.1 install. In case you install the 10.1.0.5 or higher fixpack you should be aware of the following tip published in the 3Q2019 OnDemand newsletter.
ODWEK Java API users need to update CLASSPATH
Beginning with server version 10.1.0.5, customer applications that are using the Content Manager OnDemand Web Enablement Kit (ODWEK) Java APIs will need to include the Gson jar file, with path, in the CLASSPATH for the application. The file name for Gson version 2.8.1 is gson-2.8.1.jar and can be found in the <CMOD install directory>/jars directory, where CMOD install directory is your Content Manager OnDemand installation directory.
For example, the file name for Gson version 2.8.1 is gson-2.8.1.jar. If this is the name of your most current Gson file, the CLASSPATH statement must be updated to include:
AIX:
CLASSPATH=/opt/IBM/ondemand/V10.1/jars/gson-2.8.1.jar
Linux:
CLASSPATH=/opt/ibm/ondemand/V10.1/jars/gson-2.8.1.jar
Windows:
CLASSPATH=C:\Program Files\IBM\OnDemand\V10.1\jars\gson-2.8.1.jar
IBM i
CLASSPATH=/QIBM/ProdData/OnDemand/jars/gson-2.8.1.jar.