Added empty space after '.' between two sentences.

Change-Id: I6fa88561264bffa2df568a47a9e562c4e4fe7df6
diff --git a/utils/misc/src/main/java/org/onlab/packet/Ip4Prefix.java b/utils/misc/src/main/java/org/onlab/packet/Ip4Prefix.java
index ca9fc61..819b02f 100644
--- a/utils/misc/src/main/java/org/onlab/packet/Ip4Prefix.java
+++ b/utils/misc/src/main/java/org/onlab/packet/Ip4Prefix.java
@@ -92,7 +92,7 @@
     public static Ip4Prefix valueOf(String address) {
         final String[] parts = address.split("/");
         if (parts.length != 2) {
-            String msg = "Malformed IPv4 prefix string: " + address + "." +
+            String msg = "Malformed IPv4 prefix string: " + address + ". " +
                 "Address must take form \"x.x.x.x/y\"";
             throw new IllegalArgumentException(msg);
         }