ID 228258 - Nuke 10.0 and up crashes when 'fromScript' is used on non-added knob

Problem summary
When 'fromScript()' is used without an added knob, a crash occurs in Nuke 10 and later versions.

Customer reported version

Nuke 10.0v3

Customer reported platform

n/a

Steps to reproduce

This is a regression in Nuke 10 and above.

1)  Open Nuke 10 and above and then run the following script in the editor:

b = nuke.nodes.Blur()
a = nuke.File_Knob("blah")
#b.addKnob(a)
a.fromScript('\vdefault\vtest')

2) Nuke will crash

3) Then run the same script adding the 'addKnob' line...

b = nuke.nodes.Blur()
a = nuke.File_Knob("blah")
b.addKnob(a)
a.fromScript('\vdefault\vtest')

4) The crash do not occur

5) The script in step 1 do no occur in Nuke 9.0v8 and older.

Reproduced by support

Reproduced by support in Nuke 10.0v1 (Windows 7). Just run the following script in Nuke 10.0v1 and it will crash. It doesn't in Nuke 9.0v8 and older.
I've commented out the 3rd line on purpose. If this line is enabled, then no crash occurs.

b = nuke.nodes.Blur()
a = nuke.File_Knob("blah")
#b.addKnob(a)
a.fromScript('\vdefault\vtest')

Expected behaviour
Nuke 10 no crashing when the script is run without the 'addKnob' line.

Actual behaviour
Nuke crashes unless the 'addKnob' line is added