diff --git a/lib/java-extras/src/main/java/org/triplea/java/collections/CollectionUtils.java b/lib/java-extras/src/main/java/org/triplea/java/collections/CollectionUtils.java
index 345bac69be7..9966468593e 100644
--- a/lib/java-extras/src/main/java/org/triplea/java/collections/CollectionUtils.java
+++ b/lib/java-extras/src/main/java/org/triplea/java/collections/CollectionUtils.java
@@ -12,6 +12,7 @@
 import java.util.Collection;
 import java.util.Comparator;
 import java.util.List;
+import java.util.Set;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
 import javax.annotation.Nullable;
@@ -34,7 +35,7 @@ public static <T> int countMatches(final Collection<T> collection, final Predica
     checkNotNull(collection);
     checkNotNull(predicate);
 
-    return (int) ImmutableList.copyOf(collection).stream().filter(predicate).count();
+    return (int) collection.stream().filter(predicate).count();
   }
 
   /**
@@ -49,7 +50,7 @@ public static <T> List<T> getMatches(
     checkNotNull(collection);
     checkNotNull(predicate);
 
-    return ImmutableList.copyOf(collection).stream().filter(predicate).collect(Collectors.toList());
+    return collection.stream().filter(predicate).collect(Collectors.toList());
   }
 
   /**
@@ -68,22 +69,21 @@ public static <T> List<T> getNMatches(
     checkArgument(max >= 0, "max must not be negative");
     checkNotNull(predicate);
 
-    return ImmutableList.copyOf(collection).stream()
-        .filter(predicate)
-        .limit(max)
-        .collect(Collectors.toList());
+    return collection.stream().filter(predicate).limit(max).collect(Collectors.toList());
   }
 
   /** return a such that a exists in c1 and a exists in c2. always returns a new collection. */
   public static <T> List<T> intersection(
       final Collection<T> collection1, final Collection<T> collection2) {
-    if (collection1 == null || collection2 == null) {
+    if (collection1 == null
+        || collection2 == null
+        || collection1.isEmpty()
+        || collection2.isEmpty()) {
       return new ArrayList<>();
     }
-    final Collection<T> c1 = ImmutableSet.copyOf(collection1);
-    final Collection<T> c2 = ImmutableSet.copyOf(collection2);
-
-    return c1.stream().filter(c2::contains).collect(Collectors.toList());
+    final Collection<T> c2 =
+        (collection2 instanceof Set) ? collection2 : ImmutableSet.copyOf(collection2);
+    return collection1.stream().distinct().filter(c2::contains).collect(Collectors.toList());
   }
 
   /** Returns a such that a exists in c1 but not in c2. Always returns a new collection. */
@@ -96,10 +96,9 @@ public static <T> List<T> difference(
       return new ArrayList<>(collection1);
     }
 
-    final Collection<T> c1 = ImmutableSet.copyOf(collection1);
-    final Collection<T> c2 = ImmutableSet.copyOf(collection2);
-
-    return ImmutableList.copyOf(c1).stream().filter(not(c2::contains)).collect(Collectors.toList());
+    final Collection<T> c2 =
+        (collection2 instanceof Set) ? collection2 : ImmutableSet.copyOf(collection2);
+    return collection1.stream().distinct().filter(not(c2::contains)).collect(Collectors.toList());
   }
 
   /**