bug in strrchr() - always return 0 when you search '\0' char

strrchr() - return 0 when you search '\0' char

:sample test code

void test(void)
{
    char * ptr; 
    char testString[8] = "hello";

    ptr = strrchr( testString, '\0' );

    if(ptr)
    {
        *(ptr - 1) = '~';
    }
    printf("%s\n",testString); 
}

Expected output : hell~     (Tested and works on standard libraries on windows and Linux)

Actual output:hello.  (On KEIL, Not ok)

IDE-Version:
µVision V5.28.0.0
Copyright (C) 2019 ARM Ltd and ARM Germany GmbH. All rights reserved.

Tool Version Numbers:
Toolchain: MDK Professional 5.28 (Flex) Version: 5.28.0.0
Toolchain Path: C:\Keil_MDK528a\ARM\ARMCC\Bin
C Compiler: Armcc.exe V5.06 update 6 (build 750)
Assembler: Armasm.exe V5.06 update 6 (build 750)
Linker/Locator: ArmLink.exe V5.06 update 6 (build 750)
Library Manager: ArmAr.exe V5.06 update 6 (build 750)
Hex Converter: FromElf.exe V5.06 update 6 (build 750)
CPU DLL: SARMCM3.DLL V5.28.0.0
Dialog DLL: TCM.DLL V1.36.2.0
Target DLL: STLink\ST-LINKIII-KEIL_SWO.dll V3.0.6.0
Dialog DLL: TCM.DLL V1.36.2.0