When building the project with OpenJDK 11, compilation fails with the following errors (full context omitted for brevity, there are lots of those):

error: package com.sun.org.apache.xml.internal.serialize is not visible
import com.sun.org.apache.xml.internal.serialize.OutputFormat;
...
error: package com.sun.org.apache.xml.internal.serialize is not visible
import com.sun.org.apache.xml.internal.serialize.XMLSerializer;
...
error: cannot find symbol ... BASE64Encoder().encode(encodeStringtoByte(raw));
error: cannot find symbol ... BASE64Decoder().decodeBuffer(coded);