Compiler error `no return statement in function returning non-void`

[ln-12]

I want to use this library in my PlatformIO/Arduino project unsing an Arduino Nano RP2040 Connect. Unfortunately, I get this compiler error because there are no return statements in these four functions:

.pio/libdeps/rp2040dev-unix-release/ArduinoBLE/src/utility/HCI.cpp: In member function 'virtual int HCIClass::saveNewAddress(uint8_t, uint8_t*, uint8_t*, uint8_t*)':
.pio/libdeps/rp2040dev-unix-release/ArduinoBLE/src/utility/HCI.cpp:469:1: error: no return statement in function returning non-void [-Werror=return-type]
  469 | }
      | ^
.pio/libdeps/rp2040dev-unix-release/ArduinoBLE/src/utility/HCI.cpp: In member function 'virtual int HCIClass::leAddResolvingAddress(uint8_t, uint8_t*, uint8_t*, uint8_t*)':
.pio/libdeps/rp2040dev-unix-release/ArduinoBLE/src/utility/HCI.cpp:496:1: error: no return statement in function returning non-void [-Werror=return-type]
  496 | }
      | ^
.pio/libdeps/rp2040dev-unix-release/ArduinoBLE/src/utility/HCI.cpp: In member function 'virtual int HCIClass::writeLK(uint8_t*, uint8_t*)':
.pio/libdeps/rp2040dev-unix-release/ArduinoBLE/src/utility/HCI.cpp:540:1: error: no return statement in function returning non-void [-Werror=return-type]
  540 | }
      | ^
.pio/libdeps/rp2040dev-unix-release/ArduinoBLE/src/utility/HCI.cpp: In member function 'virtual int HCIClass::readStoredLKs()':
.pio/libdeps/rp2040dev-unix-release/ArduinoBLE/src/utility/HCI.cpp:544:1: error: no return statement in function returning non-void [-Werror=return-type]
  544 | }
      | ^

Am I missing something here or how is this supposed to compile?