This fix adds a new API cass_value_is_null to our CQL library so

that we can check if a value is null or not before trying to decode
the datatype and readh the column value.
Closes-bug:#1699934

Change-Id: I884f4c275c7cb92b19884d4cc4d45f9cd3a2c8d4

src/database/cassandra/cql/cql_if.cc

@@ -921,6 +921,9 @@ std::string CassSelectFromTable(const std::string &table) {
 
 static GenDb::DbDataValue CassValue2DbDataValue(
     interface::CassLibrary *cci, const CassValue *cvalue) {
+    if (cci->CassValueIsNull(cvalue)) {
+        return GenDb::DbDataValue();
+    }
     CassValueType cvtype(cci->GetCassValueType(cvalue));
     switch (cvtype) {
       case CASS_VALUE_TYPE_ASCII:
@@ -3093,6 +3096,10 @@ CassError CassDatastaxLibrary::CassValueGetBytes(const CassValue* value,
     return cass_value_get_bytes(value, output, output_size);
 }
 
+cass_bool_t CassDatastaxLibrary::CassValueIsNull(const CassValue* value) {
+    return cass_value_is_null(value);
+}
+
 // CassInet
 CassInet CassDatastaxLibrary::CassInetInitV4(
     const cass_uint8_t* address) {

src/database/cassandra/cql/cql_lib_if.h

@@ -147,6 +147,7 @@ class CassLibrary {
         CassInet* output) = 0;
     virtual CassError CassValueGetBytes(const CassValue* value,
         const cass_byte_t** output, size_t* output_size) = 0;
+    virtual cass_bool_t CassValueIsNull(const CassValue* value) = 0;
 
     // CassInet
     virtual CassInet CassInetInitV4(const cass_uint8_t* address) = 0;
@@ -298,6 +299,7 @@ class CassDatastaxLibrary : public CassLibrary {
         CassInet* output);
     virtual CassError CassValueGetBytes(const CassValue* value,
         const cass_byte_t** output, size_t* output_size);
+    virtual cass_bool_t CassValueIsNull(const CassValue* value);
 
     // CassInet
     virtual CassInet CassInetInitV4(const cass_uint8_t* address);