java.lang.NullPointerException: Cannot invoke “org.jabref.gui.mergeentries.MergeEntries.getMergeEntry()” because “this.mergePanel” is null
at org.jabref@5.4.519/org.jabref.gui.collab.EntryChangeViewModel.makeChange(Unknown Source)
at org.jabref@5.4.519/org.jabref.gui.collab.ChangeDisplayDialog.lambda$new$2(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.control.Dialog.setResultAndClose(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.control.DialogPane.lambda$createButton$3(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.event.Event.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.Node.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.control.Button.fire(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.scene.control.inputmap.InputMap.handle(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.event.Event.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.Scene$MouseHandler.process(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.Scene.processMouseEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at java.base/java.security.AccessController.doPrivileged(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.View.notifyMouse(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.win.WinApplication._enterNestedEventLoopImpl(Native Method)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.win.WinApplication._enterNestedEventLoop(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.Application.enterNestedEventLoop(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.EventLoop.enter(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.QuantumToolkit.enterNestedEventLoop(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.stage.Stage.showAndWait(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.control.HeavyweightDialog.showAndWait(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.control.Dialog.showAndWait(Unknown Source)
at org.jabref@5.4.519/org.jabref.gui.JabRefDialogService.showCustomDialogAndWait(Unknown Source)
at org.jabref@5.4.519/org.jabref.gui.collab.DatabaseChangePane.lambda$onDatabaseChanged$1(Unknown Source)
at org.jabref.merged.module@5.4.519/org.controlsfx.control.action.Action.handle(Unknown Source)
at org.jabref.merged.module@5.4.519/org.controlsfx.control.action.Action.handle(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.event.Event.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.Node.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.control.Button.fire(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.scene.control.inputmap.InputMap.handle(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.event.Event.fireEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.Scene$MouseHandler.process(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.Scene.processMouseEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
at java.base/java.security.AccessController.doPrivileged(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.View.notifyMouse(Unknown Source)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at org.jabref.merged.module@5.4.519/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(Unknown Source)
at java.base/java.lang.Thread.run(Unknown Source)
Thank you for the log 
If we are lucky, some of the more knowledgeable coders will be able to find something within.
In the meanwhile, what exactly would we need to do to reproduce this error?
- What is the problem?
- What would you think is the desired behavior of Jabref?
Hi,
please try the latest dev version: index - powered by h5ai v0.29.0 (https://larsjung.de/h5ai/) We fixed the bug yesterday
We use app of windows 10 not linux
@xinhongri At the link you also find the portable windows and the msi installer for Windows
I have downloaded and installed the JabRef-5.5.msi from 4.1.2022.
JabRef 5.5–2022-01-03–c94bb1b
Windows 10 10.0 amd64
Java 16.0.2
JavaFX 17.0.1+1
After loading the ‘file JabRef-BibTeX.bib backup version’ no “background tasks are running” process took place unlike the previous attempts.* I then changed an entry and saved the BIB file. After saving, the following message appears again: The Library has been modified by another program.
This time I chose the alternative: Review changes and accept change. Finally the Task Jabref was then canceled with the help of the Task Manager.
*After saving the Bib file, the file JabRef-BibTeX.bib.sav.tmp with the entries was immediately available:
@Article{Abe2012,
author = {Abe, Keisuke and Nagao, Daisuke and Watanabe, Akira and Konno, Mikio},
date = {2012},
title = {Fabrication of highly refractive barium-titanate-incorporated polyimide nanocomposite films with high permittivity and thermal stability},
doi = {10.1002/pi.4285},
issn = {1097-0126},
pages = {n/a–n/a},
url = {http://dx.doi.org/10.1002/pi.4285},
abstract = {Crystalline nanoparticles of barium titanate (BT) are incorporated into polyimide (PI) to fabricate highly refractive, anti-UV-degradable nanocomposite films with high permittivity and thermal stability. For homogeneous incorporation of BT nanoparticles into the PI matrix, the BT nanoparticles are surface modified by phthalimide with the aid of a silane coupling agent as a scaffold. The PI nanocomposites are prepared by in situ polymerization in which a diphthalic anhydride and a diamine are used to form the PI matrix in the presence of the surface-modified nanoparticles. The refractive index of the transparent nanocomposite films reaches 1.85 at a nanoparticle content of 59 vol% with a high dielectric constant of ε = 37 and thermal stability up to 460 °C. Copyright © 2012 Society of Chemical Industry},
crossref = {Kim2011i; Colgate2012},
file = {Abe2012.pdf:Abe2012 - Fabrication of Highly Refractive Barium Titanate Incorporated Polyimide Nanocomposite Films with High Permittivity and Thermal Stability.pdf:PDF;suppl material:C:/Documents and Settings/kacbe/Desktop/Literatur/Abe2012a.pdf:PDF;:Uschi 04-11-2020.pdf:PDF},
journal = {Polymer International},
keywords = {nanocomposite films, permittivity, refractive index, thermal stability, transparency; high-k FILM},
owner = {Carsten},
publisher = {John Wiley & Sons, Ltd.},
timestamp = {2020-11-04},
year = {2012},
}
and thousand more entries and at the end:
3 KeywordGroup:PLED;2;keywords;PLED;0;0;1;;;;;
2 KeywordGroup:Pigments;0;keywords;pigment;0;0;0;;;;;
3 KeywordGroup:ZnS;2;keywords;ZnS;0;0;1;;;;;
4 KeywordGroup:Cu;2;keywords;Cu;0;0;1;;;;;
4 KeywordGroup:Pb;2;keywords;Pb;0;0;1;;;;;
4 KeywordGroup:Tm;2;keywords;Tm;0;0;1;;;;;
4 KeywordGroup:Mn;2;keywords;Mn;0;0;1;;;;;
4 KeywordGroup:Tb;2;keywords;Tb;0;0;1;;;;;
4 KeywordGroup:Li;1;keywords;Li;0;0;1;;;;;
4 KeywordGroup:Al;2;keywords;Al;0;0;1;;;;;
4 KeywordGroup:Ag;2;keywords;Ag;0;0;1;;;;;
2 KeywordGroup:Degradtion;2;keywords;degradation;0;0;0;;;;;
3 KeywordGroup:Powder EL;1;keywords;powder EL\;;0;0;1;;;;;
3 KeywordGroup:PLED - OLED;1;keywords;PLED\; OLED;0;0;1;;;;;
3 KeywordGroup:LEC;1;key
This file seems to contain all entries of the JabRef-BibTeX.bib DB. Where does the file come from?
These are the entries in the Event Log
Fix SSL exceptions by accepting ALL certificates
Not updating theme because it hasn’t changed
Theme set to Theme{type=DEFAULT, name=’’} with base css StyleSheet{jrt:/org.jabref/org/jabref/gui/Base.css}
Index path for C:\Users\benec\Dokumente\Literatur\Bib TeX\JabRef-BibTeX.bib is C:\Users\benec\AppData\Local\org.jabref\JabRef\0.5a
Opening: ‘C:\Users\benec\Dokumente\Literatur\Bib TeX\JabRef-BibTeX.bib’
Saving library…
Library saved
The library changed is a known bug. You can usually ignore it (Dismiss changes). We are working on solving this. Just a bit more complicated.
JabRef writes a bak and a sav file with the contents of the bib file when saving.
Intermediate status
I loaded the JabRef-BibTeX.bib file then changed one entry. message appears: The library was changed by another program and I pressed Dismiss changes and started Quit. This time the following window appeared:
Then started Jabref again and Jabref opens with:
which can only be closed with the task manager.
Meanwhile, I cross my fingers 
When you modify the bib file, sometimes, it will occur while sometimes it will not
but I want to modify instead of dismissing changes
Feel free to do that. that’s why the dialog has the options
it will report the message which shows above