diff --git a/pmd/src/main/java/net/sourceforge/pmd/RuleSetReferenceId.java b/pmd/src/main/java/net/sourceforge/pmd/RuleSetReferenceId.java
index 841df1b6e4..f9df6c6927 100644
--- a/pmd/src/main/java/net/sourceforge/pmd/RuleSetReferenceId.java
+++ b/pmd/src/main/java/net/sourceforge/pmd/RuleSetReferenceId.java
@@ -251,11 +251,13 @@ public class RuleSetReferenceId {
      */
     public static List<RuleSetReferenceId> parse(String referenceString) {
 	List<RuleSetReferenceId> references = new ArrayList<RuleSetReferenceId>();
-	if (referenceString.indexOf(',') == -1) {
-	    references.add(new RuleSetReferenceId(referenceString));
-	} else {
-	    for (String name : referenceString.split(",")) {
-		references.add(new RuleSetReferenceId(name));
+	if (referenceString != null && referenceString.trim().length() > 0) {

+	    if (referenceString.indexOf(',') == -1) {
+		references.add(new RuleSetReferenceId(referenceString));
+	    } else {
+		for (String name : referenceString.split(",")) {
+		    references.add(new RuleSetReferenceId(name));
+		}
 	    }
 	}
 	return references;
diff --git a/pmd/src/main/java/net/sourceforge/pmd/processor/AbstractPMDProcessor.java b/pmd/src/main/java/net/sourceforge/pmd/processor/AbstractPMDProcessor.java
index fa063bcd48..d17b273ea7 100644
--- a/pmd/src/main/java/net/sourceforge/pmd/processor/AbstractPMDProcessor.java
+++ b/pmd/src/main/java/net/sourceforge/pmd/processor/AbstractPMDProcessor.java
@@ -56,7 +56,7 @@ public abstract class AbstractPMDProcessor {
 			return factory.createRuleSets(configuration.getRuleSets());
 		} catch (RuleSetNotFoundException rsnfe) {
 			// should not happen: parent already created a ruleset
-			return null;
+			return new RuleSets();
 		}
 	}