The value SB-VM::GENERIC-= is not of type (OR STRING SB-DI::COMPILED-DEBUG-FUN NULL)

Not sure what's going on here.
Get the error when running profiling on my project.

```lisp
(flamegraph:save-flame-graph ("/tmp/ion.stack")
(dotimes (i 5) (init-test-world!)))
```

```
The value
SB-VM::GENERIC-=
is not of type
(OR STRING SB-DI::COMPILED-DEBUG-FUN NULL)
[Condition of type TYPE-ERROR]

Restarts:
0: [RETRY] Retry SLY mREPL evaluation request.
1: [*ABORT] Return to SLY's top level.
2: [ABORT] abort thread (#)

Backtrace:
0: ((LAMBDA (SB-PCL::|.P0.|)) #)
1: (FLAMEGRAPH::SEARCH-OR-ADD-CHILD # :calls 1> SB-VM::GENERIC-=)
Locals:
FUNC = SB-VM::GENERIC-=
NODE = # :calls 1>
2: ((LAMBDA (FLAMEGRAPH::INFO FLAMEGRAPH::PC-OR-OFFSET) :IN FLAMEGRAPH::MAKE-GRAPH) SB-VM::GENERIC-= #)
Locals:
FLAMEGRAPH::CURRENT-NODE = # :calls 1>
FLAMEGRAPH::INFO = SB-VM::GENERIC-=
3: (SB-SPROF::MAP-TRACE-PC-LOCS # (#((SB-SPROF::TRACE-START . 100) #
I = 3252
SAMPLES = #((SB-SPROF::TRACE-START . 100) # # 84 ..)
TRACE = (#((SB-SPROF::TRACE-START . 100) # # 84 ..))
4: (SB-SPROF:MAP-TRACES # #S(SB-SPROF::SAMPLES :VECTOR #<(SIMPLE-VECTOR 14538) {100162800F}> :TRACE-COUNT 128 :UNIQUE..
Locals:
END = 3364
FUNCTION = #
INDEX = 14538
SAMPLES = #S(SB-SPROF::SAMPLES ..)
VECTOR = #((SB-SPROF::TRACE-START . 100) # # 84 ..)
5: (FLAMEGRAPH::MAKE-GRAPH)
Locals:
ROOT = # :calls 0>
6: ((LAMBDA ()))
7: (SB-INT:SIMPLE-EVAL-IN-LEXENV (FLAMEGRAPH:SAVE-FLAME-GRAPH ("/tmp/ion.stack") (DOTIMES (I 5) (INIT-TEST-WORLD!))) #)
8: (EVAL (FLAMEGRAPH:SAVE-FLAME-GRAPH ("/tmp/ion.stack") (DOTIMES (I 5) (INIT-TEST-WORLD!))))
```