DB2: Fix Concat operator

ebean-core/src/main/java/io/ebeaninternal/server/expression/platform/Db2DbExpression.java

@@ -0,0 +1,13 @@
+package io.ebeaninternal.server.expression.platform;
+
+/**
+ * DB2 handling of platform specific expressions. ARRAY expressions not supported.
+ */
+final class Db2DbExpression extends BasicDbExpression {
+
+  @Override
+  public String concat(String property0, String separator, String property1, String suffix) {
+    return concatOperator(property0, separator, property1, suffix);
+  }
+
+}

ebean-core/src/main/java/io/ebeaninternal/server/expression/platform/DbExpressionHandlerFactory.java

@@ -24,6 +24,8 @@ public final class DbExpressionHandlerFactory {
         return new MySqlDbExpression();
       case ORACLE:
         return new OracleDbExpression();
+      case DB2:
+        return new Db2DbExpression();
       case SQLSERVER:
         return new SqlServerDbExpression();
       case HANA: