Apply suggestions from code review

Co-authored-by: TobiKattmann <31306376+TobiKattmann@users.noreply.github.com>

Author: pcarruscag

Common/src/CConfig.cpp

@@ -1932,6 +1932,7 @@ void CConfig::SetConfig_Options() {
 
   /*!\brief CUSTOM_OBJFUNC \n DESCRIPTION: User-provided definition of a custom objective function. \ingroup Config*/
   addStringOption("CUSTOM_OBJFUNC", CustomObjFunc, "");
+  /*!\brief CUSTOM_OUTPUTS \n DESCRIPTION: User-provided definitions for custom output. \ingroup Config*/
   addStringOption("CUSTOM_OUTPUTS", CustomOutputs, "");
 
   /* DESCRIPTION: parameter for the definition of a complex objective function */

SU2_CFD/include/output/CFlowOutput.hpp

@@ -267,7 +267,7 @@ class CFlowOutput : public CFVMOutput{
                        "E.g. this may only be a variable of the compressible solver.", CURRENT_FUNCTION);
       }
 
-      /*--- An index equal to NOT_A_VARIABLE may refer to an history output. ---*/
+      /*--- An index equal to NOT_A_VARIABLE may refer to a history output. ---*/
       output.varIndices.back() += output.otherOutputs.size();
       output.otherOutputs.push_back(GetPtrToHistoryOutput(var));
       if (output.otherOutputs.back() == nullptr) {

SU2_CFD/src/output/CFlowOutput.cpp

@@ -758,8 +758,10 @@ void CFlowOutput::SetCustomOutputs(const CSolver* const* solver, const CGeometry
             CNEMOEulerVariable::template CIndices<unsigned long>(nDim, config->GetnSpecies()), output);
       } else if (config->GetKind_Regime() == ENUM_REGIME::COMPRESSIBLE) {
         ConvertVariableSymbolsToIndices(CEulerVariable::template CIndices<unsigned long>(nDim, 0), output);
-      } else {
+      } else if (config->GetKind_Regime() == ENUM_REGIME::INCOMPRESSIBLE) {
         ConvertVariableSymbolsToIndices(CIncEulerVariable::template CIndices<unsigned long>(nDim, 0), output);
+      } else {
+        SU2_MPI::Error("Unknown flow solver type.", CURRENT_FUNCTION);
       }
       /*--- Convert marker names to their index (if any) in this rank. ---*/