Bug#21263 mysql client XML output does not distinguish between NULL and string 'NULL'

  
  Fix: "mysql --xml" now print NULL values the same way that "mysqldump --xml" does:
  
    <field name="name" xsi:nil="true" />
  
  to distinguish from empty strings:
  
    <field name="name"></field>
  
  and from string "NULL":
  
    <field name="name">NULL</field>


client/mysql.cc:
  Fixing to print NULLs differently from empty strings
mysql-test/r/client_xml.result:
  Fixing test result accordingly

client/mysql.cc

@@ -2509,9 +2509,14 @@ print_table_data_xml(MYSQL_RES *result)
     {
       tee_fprintf(PAGER, "\t<field name=\"");
       xmlencode_print(fields[i].name, (uint) strlen(fields[i].name));
-      tee_fprintf(PAGER, "\">");
-      xmlencode_print(cur[i], lengths[i]);
-      tee_fprintf(PAGER, "</field>\n");
+      if (cur[i])
+      {
+        tee_fprintf(PAGER, "\">");
+        xmlencode_print(cur[i], lengths[i]);
+        tee_fprintf(PAGER, "</field>\n");
+      }
+      else
+        tee_fprintf(PAGER, "\" xsi:nil=\"true\" />\n");
     }
     (void) tee_fputs("  </row>\n", PAGER);
   }

mysql-test/r/client_xml.result

@@ -68,7 +68,7 @@ insert into t1 values (1, 2, 'a&b a<b a>b');
 <resultset statement="select null from dual
 ">
   <row>
-	<field name="NULL">NULL</field>
+	<field name="NULL" xsi:nil="true" />
   </row>
 </resultset>
 drop table t1;