JRE emulation misses java.io.Externalizable

[xamde]

The GWT JRE emulation contains many types. In java.io.* all of them [1] are present in the J2CL JRE emulation [2] -- except one type: java.io.Externalizable is missing. I need just the type, no methods required.

[1] https://www.gwtproject.org/doc/latest/RefJreEmulation.html#Package_java_io
[2] https://github.com/google/j2cl/tree/master/jre/java/java/io

Solution
Just add an empty interface in java.io.