diff --git a/src/PostalCodes.UnitTests/PostalCodeRangeTests.cs b/src/PostalCodes.UnitTests/PostalCodeRangeTests.cs
index 35039f2..d909fe3 100644
--- a/src/PostalCodes.UnitTests/PostalCodeRangeTests.cs
+++ b/src/PostalCodes.UnitTests/PostalCodeRangeTests.cs
@@ -21,7 +21,14 @@ private static PostalCodeRange MakeRangeUS(string start, string end)
             var endPc = end != null ? new USPostalCode(end) : null;
             return new PostalCodeRange(startPc, endPc);
         }
-
+        
+        private static PostalCodeRange MakeRangeJP(string start, string end)
+        {
+            var startPc = start != null ? new JPPostalCode(start) : null;
+            var endPc = end != null ? new JPPostalCode(end) : null;
+            return new PostalCodeRange(startPc, endPc);
+        }
+        
         public static IEnumerable<ITestCaseData> CoincidesWithTestCases
         {
             get
@@ -231,6 +238,11 @@ public static IEnumerable<ITestCaseData> Contains_WithPostalCode_TestCases
                 yield return new TestCaseData(rangeUS2, new USPostalCode("28000 1235")).Returns(true);
                 yield return new TestCaseData(rangeUS3, new USPostalCode("28000")).Returns(true);
                 yield return new TestCaseData(rangeUS3, new USPostalCode("28000 1235")).Returns(true);
+
+                var rangeJP = MakeRangeJP("9000001", "9000006");
+                yield return new TestCaseData(rangeJP, new JPPostalCode("9000005")).Returns(true);
+                yield return new TestCaseData(rangeJP, new JPPostalCode("9000-005")).Returns(true);
+                yield return new TestCaseData(rangeJP, new JPPostalCode("9000007")).Returns(false);
             }
         }
 
diff --git a/src/PostalCodes/PostalCode.cs b/src/PostalCodes/PostalCode.cs
index d09a751..523acdc 100644
--- a/src/PostalCodes/PostalCode.cs
+++ b/src/PostalCodes/PostalCode.cs
@@ -143,7 +143,7 @@ internal PostalCode(PostalCodeFormat[] formats, string redundantCharacters, stri
         /// </summary>
         /// <param name="other">The other.</param>
         /// <returns><c>true</c> if [is adjacent to] [the specified other]; otherwise, <c>false</c>.</returns>
-        public bool IsAdjacentTo(PostalCode other)
+        private bool IsAdjacentTo(PostalCode other)
         {
             return other != null && Predecessor == other || Successor == other;
         }
@@ -152,19 +152,13 @@ public bool IsAdjacentTo(PostalCode other)
         /// Gets the predecessor.
         /// </summary>
         /// <value>The predecessor.</value>
-        public PostalCode Predecessor
-        {
-            get { return PredecessorImpl; }
-        }
+        public PostalCode Predecessor => PredecessorImpl;
 
         /// <summary>
         /// Gets the successor.
         /// </summary>
         /// <value>The successor.</value>
-        public PostalCode Successor
-        {
-            get { return SuccessorImpl; }
-        }
+        public PostalCode Successor => SuccessorImpl;
 
         /// <summary>
         /// Gets the predecessor implementation.
@@ -474,11 +468,7 @@ public PostalCode ExpandPostalCodeAsHighestInRange()
         /// <returns><c>true</c> if XXXX, <c>false</c> otherwise.</returns>
         public static bool AreAdjacent(PostalCode left, PostalCode right)
         {
-            if (left == null || right == null)
-            {
-                return false;
-            }
-            return left.IsAdjacentTo(right) && right.IsAdjacentTo(left);
+            return left != null && right != null && left.IsAdjacentTo(right) && right.IsAdjacentTo(left);
         }
 
         /// <summary>
diff --git a/src/PostalCodes/PostalCodeRange.cs b/src/PostalCodes/PostalCodeRange.cs
index af5b1c3..e635f3b 100644
--- a/src/PostalCodes/PostalCodeRange.cs
+++ b/src/PostalCodes/PostalCodeRange.cs
@@ -8,11 +8,6 @@ namespace PostalCodes
     /// </summary>
     public class PostalCodeRange : IEquatable<PostalCodeRange>, IComparable<PostalCodeRange>, IComparable
     {
-        /// <summary>
-        /// The lazy default
-        /// </summary>
-        private static readonly Lazy<PostalCodeRange> LazyDefault = new Lazy<PostalCodeRange>(() => new PostalCodeRange(null, null));
-
         private PostalCode _start;
         private PostalCode _end;
 
@@ -20,10 +15,7 @@ public class PostalCodeRange : IEquatable<PostalCodeRange>, IComparable<PostalCo
         /// Gets the default.
         /// </summary>
         /// <value>The default.</value>
-        public static PostalCodeRange Default
-        {
-            get { return LazyDefault.Value; }
-        }
+        public static readonly PostalCodeRange Default = new PostalCodeRange(null, null);
 
         /// <summary>
         /// Initializes a new instance of the <see cref="PostalCodeRange"/> class.
@@ -35,19 +27,17 @@ public PostalCodeRange(PostalCode start, PostalCode end)
         {
             if (start != null && end != null && start.GetType() != end.GetType())
             {
-                throw new ArgumentException(String.Format(
-                    "The start and the end of the range are from incompatible types ('{0}' & '{1}')",
-                    start.GetType(), end.GetType()));
+                throw new ArgumentException(
+                    $"The start and the end of the range are from incompatible types ('{start.GetType()}' & '{end.GetType()}')");
             }
 
             if (end != null && start != null && start > end)
             {
-                throw new ArgumentException(String.Format(
-                    "PostalCodeRange end ({0}) can't be before start ({1})", end, start));
+                throw new ArgumentException($"PostalCodeRange end ({end}) can't be before start ({start})");
             }
 
-            _start = start != null ? start.ExpandPostalCodeAsLowestInRange() : null;
-            _end = end != null ? end.ExpandPostalCodeAsHighestInRange() : null;
+            _start = start?.ExpandPostalCodeAsLowestInRange();
+            _end = end?.ExpandPostalCodeAsHighestInRange();
         }
 
         /// <summary>