You know you've dun gud when you get bytecode discrepancies in your code...

console.log

Exception in thread "main" java.lang.VerifyError: Bad return type
Exception Details:
  Location:
    ToolAccessor$1792393294.customOperator()Ljava/lang/Integer; @54: ireturn
  Reason:
    Type integer (current frame, stack[0]) is not assignable to 'java/lang/Integer' (from method signature)
  Current Frame:
    bci: @54
    flags: { }
    locals: { 'ToolAccessor$1792393294', integer, integer, integer }
    stack: { integer }
  Bytecode:
    0x0000000: 033c 033d 033e 1d2a b400 0ebe a200 29b2
    0x0000010: 0017 2ab4 000e 1d32 b600 1bb6 0021 1c03
    0x0000020: 9f00 0c84 0101 a700 09a7 0000 a700 0984
    0x0000030: 0301 a7ff d41b ac                      
  Stackmap Table:
    append_frame(@6,Integer,Integer,Integer)
    same_frame(@41)
    full_frame(@44,{Object[#2],Integer,Integer,Integer},{})
    same_frame(@47)
    same_frame(@53)