Fix warnings Dereference of null pointer

include/rapidjson/internal/itoa.h

 // Tencent is pleased to support the open source community by making RapidJSON available.
-// 
+//
 // Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
 //
 // Licensed under the MIT License (the "License"); you may not use this file except
@@ -7,9 +7,9 @@
 //
 // http://opensource.org/licenses/MIT
 //
-// Unless required by applicable law or agreed to in writing, software distributed 
-// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
-// CONDITIONS OF ANY KIND, either express or implied. See the License for the 
+// Unless required by applicable law or agreed to in writing, software distributed
+// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
+// CONDITIONS OF ANY KIND, either express or implied. See the License for the
 // specific language governing permissions and limitations under the License.
 
 #ifndef RAPIDJSON_ITOA_
@@ -37,12 +37,14 @@ inline const char* GetDigitsLut() {
 }
 
 inline char* u32toa(uint32_t value, char* buffer) {
+    RAPIDJSON_ASSERT(buffer != 0);
+
     const char* cDigitsLut = GetDigitsLut();
 
     if (value < 10000) {
         const uint32_t d1 = (value / 100) << 1;
         const uint32_t d2 = (value % 100) << 1;
-        
+
         if (value >= 1000)
             *buffer++ = cDigitsLut[d1];
         if (value >= 100)
@@ -55,13 +57,13 @@ inline char* u32toa(uint32_t value, char* buffer) {
         // value = bbbbcccc
         const uint32_t b = value / 10000;
         const uint32_t c = value % 10000;
-        
+
         const uint32_t d1 = (b / 100) << 1;
         const uint32_t d2 = (b % 100) << 1;
-        
+
         const uint32_t d3 = (c / 100) << 1;
         const uint32_t d4 = (c % 100) << 1;
-        
+
         if (value >= 10000000)
             *buffer++ = cDigitsLut[d1];
         if (value >= 1000000)
@@ -69,7 +71,7 @@ inline char* u32toa(uint32_t value, char* buffer) {
         if (value >= 100000)
             *buffer++ = cDigitsLut[d2];
         *buffer++ = cDigitsLut[d2 + 1];
-        
+
         *buffer++ = cDigitsLut[d3];
         *buffer++ = cDigitsLut[d3 + 1];
         *buffer++ = cDigitsLut[d4];
@@ -77,10 +79,10 @@ inline char* u32toa(uint32_t value, char* buffer) {
     }
     else {
         // value = aabbbbcccc in decimal
-        
+
         const uint32_t a = value / 100000000; // 1 to 42
         value %= 100000000;
-        
+
         if (a >= 10) {
             const unsigned i = a << 1;
             *buffer++ = cDigitsLut[i];
@@ -91,13 +93,13 @@ inline char* u32toa(uint32_t value, char* buffer) {
 
         const uint32_t b = value / 10000; // 0 to 9999
         const uint32_t c = value % 10000; // 0 to 9999
-        
+
         const uint32_t d1 = (b / 100) << 1;
         const uint32_t d2 = (b % 100) << 1;
-        
+
         const uint32_t d3 = (c / 100) << 1;
         const uint32_t d4 = (c % 100) << 1;
-        
+
         *buffer++ = cDigitsLut[d1];
         *buffer++ = cDigitsLut[d1 + 1];
         *buffer++ = cDigitsLut[d2];
@@ -111,6 +113,7 @@ inline char* u32toa(uint32_t value, char* buffer) {
 }
 
 inline char* i32toa(int32_t value, char* buffer) {
+    RAPIDJSON_ASSERT(buffer != 0);
     uint32_t u = static_cast<uint32_t>(value);
     if (value < 0) {
         *buffer++ = '-';
@@ -121,6 +124,7 @@ inline char* i32toa(int32_t value, char* buffer) {
 }
 
 inline char* u64toa(uint64_t value, char* buffer) {
+    RAPIDJSON_ASSERT(buffer != 0);
     const char* cDigitsLut = GetDigitsLut();
     const uint64_t  kTen8 = 100000000;
     const uint64_t  kTen9 = kTen8 * 10;
@@ -131,13 +135,13 @@ inline char* u64toa(uint64_t value, char* buffer) {
     const uint64_t kTen14 = kTen8 * 1000000;
     const uint64_t kTen15 = kTen8 * 10000000;
     const uint64_t kTen16 = kTen8 * kTen8;
-    
+
     if (value < kTen8) {
         uint32_t v = static_cast<uint32_t>(value);
         if (v < 10000) {
             const uint32_t d1 = (v / 100) << 1;
             const uint32_t d2 = (v % 100) << 1;
-            
+
             if (v >= 1000)
                 *buffer++ = cDigitsLut[d1];
             if (v >= 100)
@@ -150,13 +154,13 @@ inline char* u64toa(uint64_t value, char* buffer) {
             // value = bbbbcccc
             const uint32_t b = v / 10000;
             const uint32_t c = v % 10000;
-            
+
             const uint32_t d1 = (b / 100) << 1;
             const uint32_t d2 = (b % 100) << 1;
-            
+
             const uint32_t d3 = (c / 100) << 1;
             const uint32_t d4 = (c % 100) << 1;
-            
+
             if (value >= 10000000)
                 *buffer++ = cDigitsLut[d1];
             if (value >= 1000000)
@@ -164,7 +168,7 @@ inline char* u64toa(uint64_t value, char* buffer) {
             if (value >= 100000)
                 *buffer++ = cDigitsLut[d2];
             *buffer++ = cDigitsLut[d2 + 1];
-            
+
             *buffer++ = cDigitsLut[d3];
             *buffer++ = cDigitsLut[d3 + 1];
             *buffer++ = cDigitsLut[d4];
@@ -174,22 +178,22 @@ inline char* u64toa(uint64_t value, char* buffer) {
     else if (value < kTen16) {
         const uint32_t v0 = static_cast<uint32_t>(value / kTen8);
         const uint32_t v1 = static_cast<uint32_t>(value % kTen8);
-        
+
         const uint32_t b0 = v0 / 10000;
         const uint32_t c0 = v0 % 10000;
-        
+
         const uint32_t d1 = (b0 / 100) << 1;
         const uint32_t d2 = (b0 % 100) << 1;
-        
+
         const uint32_t d3 = (c0 / 100) << 1;
         const uint32_t d4 = (c0 % 100) << 1;
 
         const uint32_t b1 = v1 / 10000;
         const uint32_t c1 = v1 % 10000;
-        
+
         const uint32_t d5 = (b1 / 100) << 1;
         const uint32_t d6 = (b1 % 100) << 1;
-        
+
         const uint32_t d7 = (c1 / 100) << 1;
         const uint32_t d8 = (c1 % 100) << 1;
 
@@ -209,7 +213,7 @@ inline char* u64toa(uint64_t value, char* buffer) {
             *buffer++ = cDigitsLut[d4];
         if (value >= kTen8)
             *buffer++ = cDigitsLut[d4 + 1];
-        
+
         *buffer++ = cDigitsLut[d5];
         *buffer++ = cDigitsLut[d5 + 1];
         *buffer++ = cDigitsLut[d6];
@@ -222,7 +226,7 @@ inline char* u64toa(uint64_t value, char* buffer) {
     else {
         const uint32_t a = static_cast<uint32_t>(value / kTen16); // 1 to 1844
         value %= kTen16;
-        
+
         if (a < 10)
             *buffer++ = static_cast<char>('0' + static_cast<char>(a));
         else if (a < 100) {
@@ -232,7 +236,7 @@ inline char* u64toa(uint64_t value, char* buffer) {
         }
         else if (a < 1000) {
             *buffer++ = static_cast<char>('0' + static_cast<char>(a / 100));
-            
+
             const uint32_t i = (a % 100) << 1;
             *buffer++ = cDigitsLut[i];
             *buffer++ = cDigitsLut[i + 1];
@@ -245,28 +249,28 @@ inline char* u64toa(uint64_t value, char* buffer) {
             *buffer++ = cDigitsLut[j];
             *buffer++ = cDigitsLut[j + 1];
         }
-        
+
         const uint32_t v0 = static_cast<uint32_t>(value / kTen8);
         const uint32_t v1 = static_cast<uint32_t>(value % kTen8);
-        
+
         const uint32_t b0 = v0 / 10000;
         const uint32_t c0 = v0 % 10000;
-        
+
         const uint32_t d1 = (b0 / 100) << 1;
         const uint32_t d2 = (b0 % 100) << 1;
-        
+
         const uint32_t d3 = (c0 / 100) << 1;
         const uint32_t d4 = (c0 % 100) << 1;
-        
+
         const uint32_t b1 = v1 / 10000;
         const uint32_t c1 = v1 % 10000;
-        
+
         const uint32_t d5 = (b1 / 100) << 1;
         const uint32_t d6 = (b1 % 100) << 1;
-        
+
         const uint32_t d7 = (c1 / 100) << 1;
         const uint32_t d8 = (c1 % 100) << 1;
-        
+
         *buffer++ = cDigitsLut[d1];
         *buffer++ = cDigitsLut[d1 + 1];
         *buffer++ = cDigitsLut[d2];
@@ -284,11 +288,12 @@ inline char* u64toa(uint64_t value, char* buffer) {
         *buffer++ = cDigitsLut[d8];
         *buffer++ = cDigitsLut[d8 + 1];
     }
-    
+
     return buffer;
 }
 
 inline char* i64toa(int64_t value, char* buffer) {
+    RAPIDJSON_ASSERT(buffer != 0);
     uint64_t u = static_cast<uint64_t>(value);
     if (value < 0) {
         *buffer++ = '-';