make resolve() method more robust

SVN: 12593

common/source/java/ch/systemsx/cisd/common/types/BooleanOrUnknown.java

@@ -43,21 +43,26 @@ public enum BooleanOrUnknown
         return niceRepresentation;
     }
 
-    public final static BooleanOrUnknown resolve(final String niceRepresentation)
+    public final static BooleanOrUnknown resolve(final String niceRepresentationOrNull)
     {
-        if (niceRepresentation.equals("FALSE"))
+        if (niceRepresentationOrNull == null)
+        {
+            return U;
+        }
+        if (niceRepresentationOrNull.equals("FALSE"))
         {
             return F;
         }
-        if (niceRepresentation.equals("TRUE"))
+        if (niceRepresentationOrNull.equals("TRUE"))
         {
             return T;
         }
-        if (niceRepresentation.equals("UNKNOWN"))
+        if (niceRepresentationOrNull.equals("UNKNOWN"))
         {
             return U;
         }
-        throw new IllegalArgumentException(String.format("Given nice representation '%s' unknown."));
+        throw new IllegalArgumentException(String.format("Given nice representation '%s' unknown.",
+                niceRepresentationOrNull));
     }
 
     /**