What causes gcc invalid option for mtune?

I use ODB Library in my programm. By compiling I get the following message:

[  1%] Generating ../odb_gen/XXX_odb.cppcc1plus: error: bad value (‘/dev/null’) for ‘-mtune=’ switchcc1plus: error: bad value (‘/dev/null’) for ‘-mtune=’ switchcc1plus: note: valid arguments to ‘-mtune=’ switch are: nocona core2 nehalem corei7 westmere sandybridge corei7-avx ivybridge core-avx-i haswell core-avx2 broadwell skylake skylake-avx512 bonnell atom silvermont slm knl intel x86-64 eden-x2 nano nano-1000 nano-2000 nano-3000 nano-x2 eden-x4 nano-x4 k8 k8-sse3 opteron opteron-sse3 athlon64 athlon64-sse3 athlon-fx amdfam10 barcelona bdver1 bdver2 bdver3 bdver4 znver1 btver1 btver2 genericcc1plus: note: valid arguments to ‘-mtune=’ switch are: nocona core2 nehalem corei7 westmere sandybridge corei7-avx ivybridge core-avx-i haswell core-avx2 broadwell skylake skylake-avx512 bonnell atom silvermont slm knl intel x86-64 eden-x2 nano nano-1000 nano-2000 nano-3000 nano-x2 eden-x4 nano-x4 k8 k8-sse3 opteron opteron-sse3 athlon64 athlon64-sse3 athlon-fx amdfam10 barcelona bdver1 bdver2 bdver3 bdver4 znver1 btver1 btver2 genericXXXX/build.make:249: recipe for target 'odb_gen/XXX_odb.cpp' failedmake[2]: *** [odb_gen/XXX_odb.cpp] Error 1

I don't know what is the reason for this error message, therefore I don't understand how I can fix it. I would appreciate if someone can give a start point or explanation what can cause such behaviour.Thank you in advance!

PS: why was the 'mtune' option set to /dev/null?