Issue when finding a value of 'null' for a platform type in some instances

[bbaldino]

I've come across a problem where, when retrieving a platform type with a value of null, the null value won't trigger an exception (since we use a non-nullable type) and fall-through but instead will actually trickle all the way up as a supplied value.

The specific scenario where I saw this was:
I was converting the retrieval of the keepAliveStrategy enum in JVB IceConfig.kt. I had changed it from the old method of doing retrieving as a string and converting via KeepAliveStrategy.fromString:

retrieve("videobridge.ice.keep-alive-strategy"
    .from(JitsiConfig.newConfig)
    .asType<String>()
    .andConvertBy { KeepAliveStrategy.fromString(it) }
)

to retrieving the enum directly:

retrieve("videobridge.ice.keep-alive-strategy".from(JitsiConfig.newConfig))

but I didn't want to break support for old config files, so needed to support both. I put the 'old' parsing first, so that it would get null and fail if the string didn't match, but instead the null was used as the final value. I filed a bug, so something may come from that.