Get rid of NULLs in core/

core/fxcrt/fx_basic_gcc.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include <cctype>
 #include <cwctype>
 #include <limits>
 
@@ skipping 120 matching lines @@
 #if _FXM_PLATFORM_ != _FXM_PLATFORM_WINDOWS_
 #ifdef __cplusplus
 extern "C" {
 #endif
 FXSYS_FILE* FXSYS_wfopen(const FX_WCHAR* filename, const FX_WCHAR* mode) {
   return FXSYS_fopen(CFX_ByteString::FromUnicode(filename).c_str(),
                      CFX_ByteString::FromUnicode(mode).c_str());
 }
 char* FXSYS_strlwr(char* str) {
   if (!str) {
-    return NULL;
+    return nullptr;
   }
   char* s = str;
   while (*str) {
     *str = FXSYS_tolower(*str);
     str++;
   }
   return s;
 }
 char* FXSYS_strupr(char* str) {
   if (!str) {
-    return NULL;
+    return nullptr;
   }
   char* s = str;
   while (*str) {
     *str = FXSYS_toupper(*str);
     str++;
   }
   return s;
 }
 FX_WCHAR* FXSYS_wcslwr(FX_WCHAR* str) {
   if (!str) {
-    return NULL;
+    return nullptr;
   }
   FX_WCHAR* s = str;
   while (*str) {
     *str = FXSYS_tolower(*str);
     str++;
   }
   return s;
 }
 FX_WCHAR* FXSYS_wcsupr(FX_WCHAR* str) {
   if (!str) {
-    return NULL;
+    return nullptr;
   }
   FX_WCHAR* s = str;
   while (*str) {
     *str = FXSYS_toupper(*str);
     str++;
   }
   return s;
 }
 int FXSYS_stricmp(const char* dst, const char* src) {
   int f, l;
@@ skipping 60 matching lines @@
       buf[wlen] = bstr[i];
     }
     wlen++;
   }
   return wlen;
 }
 #ifdef __cplusplus
 }
 #endif
 #endif