Cannot load com.sun.java.swing.plaf.gtk.GTKLookAndFeel

hi,

When I start the portable version of IDE, I get the following message:

~/arduino-1.8.5$ sudo -s <<< ./arduino
Picked up JAVA_TOOL_OPTIONS:
java.lang.Error: Cannot load com.sun.java.swing.plaf.gtk.GTKLookAndFeel
at javax.swing.UIManager.initializeDefaultLAF(UIManager.java:1351)
at javax.swing.UIManager.initialize(UIManager.java:1459)
at javax.swing.UIManager.maybeInitialize(UIManager.java:1426)
at javax.swing.UIManager.getLookAndFeel(UIManager.java:492)
at processing.app.linux.GTKLookAndFeelFixer.installGtkPopupBugWorkaround(GTKLookAndFeelFixer.java:79)
at processing.app.linux.Platform.setLookAndFeel(Platform.java:41)
at processing.app.Base.(Base.java:224)
at processing.app.Base.main(Base.java:144)

Java Oracle 8 is installed on my Ubuntu 17.10 machine

java version "1.8.0_151"
Java(TM) SE Runtime Environment (build 1.8.0_151-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.151-b12, mixed mode)

A previous java OpenJDK version has been removed

is this someone would have an idea, solution,... ?

Thank you in advance for your help