[MC-134136] 1.12.2 world resets in 1.13

When attempting to optimise a world created in 1.12.2 into 1.13 the readout indicates 'Failed' before optimising a single chunk. When the world is opened it generates the world as it was brand new, deleting all my builds.

When I try to open the world without optimisation the same thing occurs, I am spawned in my last position, but the world has regenerated to an 'as new' state.

When attempting to Optimise - Game output error reads:

Error upgrading world
java.lang.NullPointerException
at bwg.a(SourceFile:138)
at bwg.a(SourceFile:81)
at bnm.a(SourceFile:107)
at bnm.a(SourceFile:822)
at acx.o(SourceFile:89)
at java.lang.Thread.run(Thread.java:745)

Complete log of both situations attached.