fix un initialized attribute

contribs/application/src/main/java/org/matsim/application/prepare/population/SplitActivityTypesDuration.java

@@ -13,6 +13,7 @@
 import picocli.CommandLine;
 
 import java.nio.file.Path;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Objects;
 import java.util.Set;
@@ -47,7 +48,7 @@ public class SplitActivityTypesDuration implements MATSimAppCommand, PersonAlgor
 	private String subpopulation;
 
 	@CommandLine.Option(names = "--exclude", description = "Activity types that won't be split", split = ",", defaultValue = "")
-	private Set<String> exclude;
+	private Set<String> exclude = new HashSet<>();
 
 
 	/**
@@ -65,6 +66,13 @@ public SplitActivityTypesDuration(int activityBinSize, int maxTypicalDuration, i
 		this.endTimeToDuration = endTimeToDuration;
 	}
 
+	/**
+	 * Set activity types to be excluded from splitting.
+	 */
+	public void setExclude(Set<String> exclude) {
+		this.exclude = exclude;
+	}
+
 	public static void main(String[] args) {
 		new SplitActivityTypesDuration().execute(args);
 	}