Use SubMonintor in CheckConditionsContext

done() call not necessary here and convert can also handle null.  Also
split will also check for cancellation so the additional cancellation
check is not necessary.

See https://www.eclipse.org/articles/Article-Progress-Monitors/article.html

bundles/org.eclipse.ltk.core.refactoring/src/org/eclipse/ltk/core/refactoring/participants/CheckConditionsContext.java

@@ -22,8 +22,6 @@
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.IStatus;
-import org.eclipse.core.runtime.NullProgressMonitor;
-import org.eclipse.core.runtime.OperationCanceledException;
 import org.eclipse.core.runtime.Status;
 import org.eclipse.core.runtime.SubMonitor;
 
@@ -102,8 +100,7 @@ public void add(IConditionChecker checker) throws CoreException {
 	 * @throws CoreException if an error occurs during condition checking
 	 */
 	public RefactoringStatus check(IProgressMonitor pm) throws CoreException {
-		if (pm == null)
-			pm= new NullProgressMonitor();
+
 		RefactoringStatus result= new RefactoringStatus();
 		mergeResourceOperationAndValidateEdit();
 		List<IConditionChecker> values= new ArrayList<>(fCheckers.values());
@@ -117,13 +114,11 @@ public RefactoringStatus check(IProgressMonitor pm) throws CoreException {
 				return 1;
 			return 0;
 		});
+
 		SubMonitor sm= SubMonitor.convert(pm, "", values.size()); //$NON-NLS-1$
 		for (IConditionChecker checker : values) {
 			result.merge(checker.check(sm.split(1)));
-			if (pm.isCanceled())
-				throw new OperationCanceledException();
 		}
-		pm.done();
 		return result;
 	}