Terraria mod isn't building

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C#

I got the source code for a mod called Elemental Hearts Recrafted. And I wanted to edit some features. But when I try to build I get this error. I don't know much about coding.

[20:07:27] [Thread Pool Worker/ERROR] [tML]: Value cannot be null.
Parameter name: document
System.ArgumentNullException: Value cannot be null.
Parameter name: document
  at Mono.Cecil.Cil.SequencePoint..ctor (Int32 offset, Document document) [0x00009] in data-0x7f933ab64000 
  at Mono.Cecil.SignatureReader.ReadSequencePoints (Document document) [0x000f9] in data-0x7f933ab64000 
  at Mono.Cecil.MetadataReader.ReadSequencePoints (MethodDefinition method) [0x0004e] in data-0x7f933ab64000 
  at Mono.Cecil.Cil.PortablePdbReader.ReadSequencePoints (MethodDebugInformation method_info) [0x00000] in data-0x7f933ab64000 
  at Mono.Cecil.Cil.PortablePdbReader.Read (MethodDefinition method) [0x00007] in data-0x7f933ab64000 
  at Mono.Cecil.ImmediateModuleReader.ReadMethodsSymbols (TypeDefinition type, ISymbolReader symbol_reader) [0x0003d] in data-0x7f933ab64000 
  at Mono.Cecil.ImmediateModuleReader.ReadTypesSymbols (Collection[T] types, ISymbolReader symbol_reader) [0x00029] in data-0x7f933ab64000 
  at Mono.Cecil.ImmediateModuleReader.ReadTypesSymbols (Collection[T] types, ISymbolReader symbol_reader) [0x0001b] in data-0x7f933ab64000 
  at Mono.Cecil.ImmediateModuleReader.ReadTypesSymbols (Collection[T] types, ISymbolReader symbol_reader) [0x0001b] in data-0x7f933ab64000 
  at Mono.Cecil.ImmediateModuleReader.ReadSymbols (ModuleDefinition module) [0x00010] in data-0x7f933ab64000 
  at Mono.Cecil.ModuleWriter.Write (ModuleDefinition module, Disposable[T] stream, WriterParameters parameters) [0x00039] in data-0x7f933ab64000 
  at Mono.Cecil.ModuleWriter.WriteModule (ModuleDefinition module, Disposable[T] stream, WriterParameters parameters) [0x00002] in data-0x7f933ab64000 
  at Mono.Cecil.ModuleDefinition.Write (String fileName, WriterParameters parameters) [0x00017] in data-0x7f933ab64000 
  at Mono.Cecil.AssemblyDefinition.Write (String fileName, WriterParameters parameters) [0x00000] in data-0x7f933ab64000 
  at Terraria.ModLoader.Core.ModCompile.BuildModForPlatform (BuildingMod mod, Boolean xna) [0x0025d] in tModLoader.exe 
  at Terraria.ModLoader.Core.ModCompile.Build (BuildingMod mod) [0x000d0] in tModLoader.exe 
  at Terraria.ModLoader.Core.ModCompile.Build (String modFolder) [0x00008] in tModLoader.exe 
  at Terraria.ModLoader.UI.UIBuildMod+<>c__DisplayClass5_0.<Build>b__0 (ModCompile mc) [0x00000] in tModLoader.exe 
  at Terraria.ModLoader.UI.UIBuildMod.BuildMod (Action[T] buildAction, Boolean reload) [0x0003a] in tModLoader.exe

What I have tried:

I tried searching the folder for null and changed it but the same error came up.