Fix ddl and dml

Tarantol connector do not send any `metadata` and `rows` in case
of SQL ddl and dml.

Before this patch absence of those attributes lead to a
NullPointerException.

Closes #39

Author: Khatskevich

src/main/java/org/tarantool/JDBCBridge.java

@@ -22,7 +22,11 @@ protected JDBCBridge(TarantoolConnection connection) {
 
     protected JDBCBridge(List<TarantoolBase.SQLMetaData> sqlMetadata, List<List<Object>> rows) {
         this.sqlMetadata = sqlMetadata;
-        this.rows = rows;
+	if (rows == null) {
+	    this.rows = Collections.emptyList();
+	} else {
+	    this.rows = rows;
+	}
         columnsByName = new LinkedHashMap<String, Integer>((int) Math.ceil(sqlMetadata.size() / 0.75), 0.75f);
         for (int i = 0; i < sqlMetadata.size(); i++) {
             columnsByName.put(sqlMetadata.get(i).getName(), i + 1);

src/main/java/org/tarantool/TarantoolBase.java

@@ -10,6 +10,7 @@
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.EnumMap;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -161,6 +162,9 @@ public String toString() {
 
     protected List<SQLMetaData> getSQLMetadata() {
         List<Map<Integer, Object>> meta = (List<Map<Integer, Object>>) body.get(Key.SQL_METADATA.getId());
+	if (meta == null){
+	        return Collections.emptyList();
+	}
         List<SQLMetaData> values = new ArrayList<SQLMetaData>(meta.size());
         for(Map<Integer,Object> c:meta ) {
            values.add(new SQLMetaData((String) c.get(Key.SQL_FIELD_NAME.getId())));