JSON reader fails in case of empty extern field

[mikir]

What version of Zserio and what language are you using?
Zserio: 2.13.0
Language: Python, Java, C++

Describe the bug
If JSON file contains empty extern field, e.g.

"myExternData": {
                    "buffer": [
                    ],
                    "bitSize": 0
                }

the JSON reader in Python throws exception:

zserio.exception.PythonRuntimeException: JsonReader: Unexpected end in Bit Buffer!

To Reproduce
Just create schema with empty extern field, write it to JSON and read it again.

Expected behavior
No exception.

Additional context:
When an arbitrary entry in the extern data buffer is added (to buffer array) leaving the bitsize=0, then everything works fine. The same problem is for C++ and Java.