Decompiler issue on AM2R

[Miepee]

UTMT 0.4.0.4 has a slight issue trying to decompile AM2R. gml_Script_spawn_random_septogg in particular.

/* EXCEPTION!
   System.NullReferenceException: Object reference not set to an instance of an object.
   at UndertaleModLib.Decompiler.Decompiler.ComputeReverseDominators(Dictionary`2 blocks, Block entryBlock) in D:\a\UndertaleModTool\UndertaleModTool\UndertaleModLib\Decompiler\Decompiler.cs:line 3124
   at UndertaleModLib.Decompiler.Decompiler.HLDecompile(DecompileContext context, Dictionary`2 blocks, Block entryPoint, Block rootExitPoint) in D:\a\UndertaleModTool\UndertaleModTool\UndertaleModLib\Decompiler\Decompiler.cs:line 3466
   at UndertaleModLib.Decompiler.Decompiler.Decompile(UndertaleCode code, GlobalDecompileContext globalContext) in D:\a\UndertaleModTool\UndertaleModTool\UndertaleModLib\Decompiler\Decompiler.cs:line 3556
   at UndertaleModTool.UndertaleCodeEditor.<>c__DisplayClass31_0.<DecompileCode>b__1() in D:\a\UndertaleModTool\UndertaleModTool\UndertaleModTool\Editors\UndertaleCodeEditor.xaml.cs:line 444
*/

Source code for that script can be found here

[Miepee]

For reference, DogScepter is able to decompile it correctly.

To be more exact about the issue, it happens in this do while loop in Decompiler.cs (starting line 3100)

            do
            {
                changed = false;
                for (int i = 0; i < blockList.Length; i++)
                {
                    if (i == entryBlockId)
                        continue;

                    Block b = blockList[i];

                    IEnumerable<Block> e;
                    if (b.conditionalExit)
                    {
                        reverseUse2[0] = b.nextBlockTrue;
                        reverseUse2[1] = b.nextBlockFalse;
                        e = reverseUse2;
                    }
                    else
                    {
                        reverseUse1[0] = b.nextBlockTrue;
                        e = reverseUse1;
                    }

                    foreach (Block pred in e)
                        changed |= dominators[i].And(dominators[pred._CachedIndex], i);
                }
            } while (changed);

Issue occurs on i==46.
b gets this value assigned:

And due to nextBlockTrue and nextBlockFalse both being null, that screws with e, as it gets this assignment then:

The foreach goes through e, assigns null to pred, and then crashes while trying to get pred._CachedIndex.