implement clang-tidy fixes

src/AMOEBA/pair_amoeba.cpp

@@ -843,7 +843,7 @@ void PairAmoeba::init_style()
     } else {
       index[i] = atom->find_custom(names[i], flag, cols);
     }
-    std::string err = "";
+    std::string err;
     if (index[i] < 0) err = "was not defined";
     else if (flag_check[i] != flag) err = "has the wrong type";
     else if (cols_check[i] != cols) err = "has the wrong number of columns";

src/lammps.cpp

@@ -150,7 +150,7 @@ LAMMPS::LAMMPS(int narg, char **arg, MPI_Comm communicator) :
   if (has_git_info() && ((update_string == " - Development") || (update_string == " - Maintenance")))
     update_string += fmt::format(" - {}", git_descriptor());
 
-  external_comm = 0;
+  external_comm = MPI_COMM_NULL;
   mdicomm = nullptr;
 
   skiprunflag = 0;
@@ -807,7 +807,7 @@ LAMMPS::~LAMMPS() noexcept(false)
   // free a copy of uorig here, so check in universe destructor will still work
 
   MPI_Comm copy = universe->uorig;
-  if (external_comm) MPI_Comm_free(&copy);
+  if (external_comm != MPI_COMM_NULL) MPI_Comm_free(&copy);
 
   delete input;
   delete universe;

unittest/formats/test_molecule_file.cpp

@@ -147,7 +147,7 @@ protected:
         fclose(fp);
 
         command(fmt::format("molecule {} {} {}", name, file, args));
-        platform::unlink(file.c_str());
+        platform::unlink(file);
     }
 };