My cmd output:
[Sun Jun 23 10:41:00 CEST 2019] [Launcher] Java version: 1.8.0_202, specificatio
n: 1.8, VM name: OpenJDK 64-Bit Server VM, VM vendor: BellSoft
[Sun Jun 23 10:41:00 CEST 2019] [Launcher] Current JAVA_HOME for running instanc
e: G:\Program Files\MCreator\MCreator183\jdk\jre
[Sun Jun 23 10:41:02 CEST 2019] [Launcher] Installation path: G:\Program Files\M
Creator\MCreator183
[Sun Jun 23 10:41:02 CEST 2019] [Launcher] User home of MCreator: G:\Users\LowPCUserxD
\.mcreator\
[Sun Jun 23 10:41:02 CEST 2019] java.io.FileNotFoundException: .\user\workspace\
workspace.settings (SystÚm nem˘×e nßjsŁ zadan˙ cestu)
[Sun Jun 23 10:41:03 CEST 2019] at java.io.FileOutputStream.open0(Native
Method)
[Sun Jun 23 10:41:03 CEST 2019] at java.io.FileOutputStream.open(FileOut
putStream.java:270)
[Sun Jun 23 10:41:03 CEST 2019] at java.io.FileOutputStream.<init>(FileO
utputStream.java:213)
[Sun Jun 23 10:41:03 CEST 2019] at java.io.FileOutputStream.<init>(FileO
utputStream.java:162)
[Sun Jun 23 10:41:03 CEST 2019] at java.io.FileWriter.<init>(FileWriter.
java:90)
[Sun Jun 23 10:41:03 CEST 2019] at co.pylo.mcreator.e.b.a(SourceFile:66)
[Sun Jun 23 10:41:03 CEST 2019] at co.pylo.mcreator.a.f(SourceFile:1618)
[Sun Jun 23 10:41:03 CEST 2019] at co.pylo.mcreator.Launcher.main(Source
File:148)
[Sun Jun 23 10:41:03 CEST 2019] Error writing .\user\workspace\workspace.setting
s (SystÚm nem˘×e nßjsŁ zadan˙ cestu)
[Sun Jun 23 10:41:03 CEST 2019] java.io.FileNotFoundException: .\user\workspace\
workspace.settings (SystÚm nem˘×e nßjsŁ zadan˙ cestu)
[Sun Jun 23 10:41:03 CEST 2019] at java.io.FileInputStream.open0(Native
Method)
[Sun Jun 23 10:41:03 CEST 2019] at java.io.FileInputStream.open(FileInpu
tStream.java:195)
[Sun Jun 23 10:41:03 CEST 2019] at java.io.FileInputStream.<init>(FileIn
putStream.java:138)
[Sun Jun 23 10:41:03 CEST 2019] at java.io.FileInputStream.<init>(FileIn
putStream.java:93)
[Sun Jun 23 10:41:03 CEST 2019] at co.pylo.mcreator.a.f(SourceFile:1624)
[Sun Jun 23 10:41:03 CEST 2019] at co.pylo.mcreator.Launcher.main(Source
File:148)
[Sun Jun 23 10:41:04 CEST 2019] [WebIO] Reading from URL: https://mcreator.net/a
pp
[Sun Jun 23 10:41:06 CEST 2019] Skipping update message ...
[Sun Jun 23 10:41:06 CEST 2019] [WebIO] Reading from URL: https://mcreator.net/a
pp/motw
[Sun Jun 23 10:41:06 CEST 2019] [WebIO] Reading from URL: https://mcreator.net/a
pp/news
[Sun Jun 23 10:41:11 CEST 2019] Failed to load import format classes! Ignore thi
s if this is the first time setup.
[Sun Jun 23 10:41:11 CEST 2019] Exception in thread "AWT-EventQueue-0" [Sun Jun
23 10:41:11 CEST 2019] java.lang.NullPointerException
[Sun Jun 23 10:41:11 CEST 2019] at co.pylo.mcreator.a.<init>(SourceFile:
601)
[Sun Jun 23 10:41:11 CEST 2019] at co.pylo.mcreator.Launcher.lambda$main
$1(SourceFile:151)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.event.InvocationEvent.dispat
ch(InvocationEvent.java:311)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventQueue.dispatchEventImpl
(EventQueue.java:758)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventQueue.access$500(EventQ
ueue.java:97)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventQueue$3.run(EventQueue.
java:709)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventQueue$3.run(EventQueue.
java:703)
[Sun Jun 23 10:41:11 CEST 2019] at java.security.AccessController.doPriv
ileged(Native Method)
[Sun Jun 23 10:41:11 CEST 2019] at java.security.ProtectionDomain$JavaSe
curityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventQueue.dispatchEvent(Eve
ntQueue.java:728)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventDispatchThread.pumpOneE
ventForFilters(EventDispatchThread.java:205)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventDispatchThread.pumpEven
tsForFilter(EventDispatchThread.java:116)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventDispatchThread.pumpEven
tsForHierarchy(EventDispatchThread.java:105)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventDispatchThread.pumpEven
ts(EventDispatchThread.java:101)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventDispatchThread.pumpEven
ts(EventDispatchThread.java:93)
[Sun Jun 23 10:41:11 CEST 2019] at java.awt.EventDispatchThread.run(Even
tDispatchThread.java:82)
You most likely forcefully closed MCreator. You can find backups of workspace.mcreator file in <install dir>/forge/.mcreator folder. Try replacing mcreator.workspace with one of the backups.
In 1.9.0 this should not be happening anymore.