[Java] Fix empty group display

Change-Id: I6f20831701069dddcfb40f8702c03f0483f0d01b

Author: xdaragon

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/java/JavaGenerator.java

@@ -2535,12 +2535,15 @@ private StringBuilder appendDecoderDisplay(
 
             append(sb, indent, "builder.append(\"" + groupName + Separators.KEY_VALUE + Separators.BEGIN_GROUP + "\");");
             append(sb, indent, groupDecoderName + " " + groupName + " = " + groupName + "();");
-            append(sb, indent, "while (" + groupName + ".hasNext())");
+            append(sb, indent, "if (" + groupName + ".count() > 0)");
             append(sb, indent, "{");
-            append(sb, indent, "    " + groupName + ".next().appendTo(builder);");
-            Separators.ENTRY.appendToGeneratedBuilder(sb, indent + INDENT, "builder");
+            append(sb, indent, "    while (" + groupName + ".hasNext())");
+            append(sb, indent, "    {");
+            append(sb, indent, "        " + groupName + ".next().appendTo(builder);");
+            Separators.ENTRY.appendToGeneratedBuilder(sb, indent + INDENT + INDENT, "builder");
+            append(sb, indent, "    }");
+            append(sb, indent, "    builder.setLength(builder.length() - 1);");
             append(sb, indent, "}");
-            append(sb, indent, "builder.setLength(builder.length() - 1);");
             append(sb, indent, "builder.append(\"" + Separators.END_GROUP + Separators.FIELD + "\");");
 
             i = findEndSignal(groups, i, Signal.END_GROUP, groupToken.name());

sbe-tool/src/test/java/uk/co/real_logic/sbe/generation/java/ToStringTest.java

@@ -1,5 +1,6 @@
 package uk.co.real_logic.sbe.generation.java;
 
+import org.agrona.concurrent.UnsafeBuffer;
 import org.junit.Test;
 import uk.co.real_logic.sbe.EncodedCarTestBase;
 
@@ -36,4 +37,20 @@ public void exampleMessagePrinted() throws Exception
                 "make=Honda|model=Civic VTi|activationCode=|",
                 result);
     }
+
+    @Test
+    public void emptyMessagePrinted() throws Exception
+    {
+        final ByteBuffer encodedMsgBuffer = ByteBuffer.allocateDirect(MSG_BUFFER_CAPACITY);
+        CAR.wrap(new UnsafeBuffer(encodedMsgBuffer), 0);
+
+        final String result = CAR.toString();
+        assertEquals(
+                "[Car]" +
+                "(sbeTemplateId=1|sbeSchemaId=1|sbeSchemaVersion=0|sbeBlockLength=45):" +
+                "serialNumber=0|modelYear=0|available=F|code=NULL_VAL|someNumbers=[0,0,0,0,0]|vehicleCode=|extras={}|" +
+                "engine=(capacity=0|numCylinders=0|manufacturerCode=|)|" +
+                "fuelFigures=[]|performanceFigures=[]|make=|model=|activationCode=|",
+                result);
+    }
 }