Table with a null partition value throws NPE

[mofojed]

Reported with https://deephaven.atlassian.net/browse/DH-16595

Table throws NPE:

LogProxy.js:87 [IrisGrid] TypeError: java.lang.NullPointerException
    at NullPointerException.createError_0 [as createError] (irisapi.nocache.js:1541:10)
    at NullPointerException.initializeBackingError (irisapi.nocache.js:1329:46)
    at NullPointerException.Throwable (irisapi.nocache.js:1268:8)
    at NullPointerException.Exception (irisapi.nocache.js:1341:16)
    at NullPointerException.RuntimeException (irisapi.nocache.js:1366:16)
    at NullPointerException.JsException (irisapi.nocache.js:1515:23)
    at new NullPointerException (irisapi.nocache.js:1528:18)
    at Object.requireNonNull (irisapi.nocache.js:52632:16)
    at Object.ofString_0 [as ofString] (irisapi.nocache.js:16421:6)
    at lm.updatePartition (IrisGrid.js:1256:76)
    at IrisGrid.js:1230:17
    at Generator.next (<anonymous>)
    at gTe (IrisGrid.js:1:99)
    at o (IrisGrid.js:2:194)
isEnabled.console.error @ LogProxy.js:87
LogProxy.js:87 [IrisGridPanel] TypeError: java.lang.NullPointerException
    at NullPointerException.createError_0 [as createError] (irisapi.nocache.js:1541:10)
    at NullPointerException.initializeBackingError (irisapi.nocache.js:1329:46)
    at NullPointerException.Throwable (irisapi.nocache.js:1268:8)
    at NullPointerException.Exception (irisapi.nocache.js:1341:16)
    at NullPointerException.RuntimeException (irisapi.nocache.js:1366:16)
    at NullPointerException.JsException (irisapi.nocache.js:1515:23)
    at new NullPointerException (irisapi.nocache.js:1528:18)
    at Object.requireNonNull (irisapi.nocache.js:52632:16)
    at Object.ofString_0 [as ofString] (irisapi.nocache.js:16421:6)
    at lm.updatePartition (IrisGrid.js:1256:76)
    at IrisGrid.js:1230:17
    at Generator.next (<anonymous>)
    at gTe (IrisGrid.js:1:99)
    at o (IrisGrid.js:2:194)

[mofojed]

Not reproducible on Community with a table with null key values:

from deephaven import new_table
from deephaven.column import string_col, int_col

source = new_table([
    string_col("X", ["A", "B", None, "C", "B", None, "B", "B", "C"]),
    string_col("Y", ["M", "N", "O", "N", "P", "M", "O", "P", "M"]),
    int_col("Number", [55, 76, 20, 130, 230, 50, 73, 137, 214]),
])

partitioned_table = source.partition_by(by="X")

There must be something else going on