Fix issue caused by illegal, empty <transporters> blocks.

It appears that we have been writing empty <transporters> blocks
into every vehicle for the past 6 or so years.  These blocks should
not exist in, e.g., combat vehicles, but apparently went unnoticed
due to loose handling of the relevant block when empty.

This change adds a new test prior to processing these empty blocks
on file load, a function to support this test, and a conditional
around writing the <transporters> block to prevent writing empty
blocks in every .BLK file.

megamek/src/megamek/common/loaders/BLKFile.java

@@ -597,16 +597,20 @@ public static BuildingBlock getBlock(Entity t) {
 
  blk.writeBlockData("motion_type", t.getMovementModeAsString());
 
- String[] transporter_array = new String[t.getTransports().size()];
- int index = 0;
- for (Transporter transporter : t.getTransports()) {
- transporter_array[index] = transporter.toString();
- if (t.isPodMountedTransport(transporter)) {
- transporter_array[index] += ":omni";
+ if(t.getTransports().size() > 0) {
+ // We should only write the transporters block for units that can and do
+ // have transporter bays. Empty Transporters blocks cause issues.
+ String[] transporter_array = new String[t.getTransports().size()];
+ int index = 0;
+ for (Transporter transporter : t.getTransports()) {
+ transporter_array[index] = transporter.toString();
+ if (t.isPodMountedTransport(transporter)) {
+ transporter_array[index] += ":omni";
+ }
+ index++;
  }
- index++;
+ blk.writeBlockData("transporters", transporter_array);
  }
- blk.writeBlockData("transporters", transporter_array);
 
  if (!t.isConventionalInfantry()) {
  if (t instanceof Aero) {
@@ -1105,7 +1109,7 @@ public static void encode(String fileName, Entity t) {
  }
 
  protected void addTransports(Entity e) throws EntityLoadingException {
- if (dataFile.exists("transporters")) {
+ if (dataFile.exists("transporters") && dataFile.containsData("transporters")) {
  String[] transporters = dataFile.getDataAsString("transporters");
  HashSet<Integer> usedBayNumbers = new HashSet<>();
 

megamek/src/megamek/common/util/BuildingBlock.java

@@ -707,4 +707,20 @@ public boolean exists(String blockName) {
 
  return true;
  }
+
+ /**
+ * Checks if a block exists and has data.
+ */
+ public boolean containsData(String blockName) {
+ if(!exists(blockName)){
+ return false;
+ }
+ // If the end index is the next line after the start index,
+ // the block is empty.
+ // Otherwise it contains data.
+ int start = findStartIndex(blockName);
+ int end = findEndIndex(blockName);
+ return (end - start) > 1;
+
+ }
 }