Avoid npe + fix name validator

Conflicts:
	bundles/plugins/org.bonitasoft.studio.expression.editor/src/org/bonitasoft/studio/expression/editor/provider/ExpressionComparator.java
	bundles/plugins/org.bonitasoft.studio.expression.editor/src/org/bonitasoft/studio/expression/editor/viewer/ExpressionViewer.java