diff --git a/mysql-test/r/timezone2.result b/mysql-test/r/timezone2.result
index 70f5ef9edc1..0ac4ddca277 100644
--- a/mysql-test/r/timezone2.result
+++ b/mysql-test/r/timezone2.result
@@ -326,5 +326,11 @@ NULL
 Warnings:
 Warning	1292	Incorrect datetime value: '00:00:00'
 #
+# MDEV-5506 safe_mutex: Trying to lock unitialized mutex at safemalloc.c on server shutdown after SELECT with CONVERT_TZ
+#
+SELECT CONVERT_TZ('2001-10-08 00:00:00', MAKE_SET(0,'+01:00'), '+00:00' );
+CONVERT_TZ('2001-10-08 00:00:00', MAKE_SET(0,'+01:00'), '+00:00' )
+NULL
+#
 # End of 5.3 tests
 #
diff --git a/mysql-test/t/date_formats.test b/mysql-test/t/date_formats.test
index 7e6990f4754..972543aefc2 100644
--- a/mysql-test/t/date_formats.test
+++ b/mysql-test/t/date_formats.test
@@ -32,6 +32,8 @@ ORDER BY variable_name;
 # SET date_format='%d.%m.%Y';
 # SET date_format='%m-%d-%Y';
 # 
+# --error ER_WRONG_VALUE_FOR_VAR
+# SET datetime_format= NULL;
 # set datetime_format= '%Y%m%d%H%i%s';
 # set datetime_format= '%Y-%m-%d %H:%i:%s';
 # set datetime_format= '%m-%d-%y %H:%i:%s.%f';
diff --git a/mysql-test/t/timezone2.test b/mysql-test/t/timezone2.test
index 7764b39bf33..2d61c7631f2 100644
--- a/mysql-test/t/timezone2.test
+++ b/mysql-test/t/timezone2.test
@@ -297,6 +297,12 @@ DROP TABLE t1;
 SELECT CONVERT_TZ(TIME('00:00:00'),'+00:00','+7:5');
 SELECT CONVERT_TZ(TIME('2010-01-01 00:00:00'),'+00:00','+7:5');
 
+--echo #
+--echo # MDEV-5506 safe_mutex: Trying to lock unitialized mutex at safemalloc.c on server shutdown after SELECT with CONVERT_TZ
+--echo #
+SELECT CONVERT_TZ('2001-10-08 00:00:00', MAKE_SET(0,'+01:00'), '+00:00' ); 
+
+
 --echo #
 --echo # End of 5.3 tests
 --echo #
diff --git a/sql/item_strfunc.cc b/sql/item_strfunc.cc
index fc0d3beeea3..1b0f8c6acc0 100644
--- a/sql/item_strfunc.cc
+++ b/sql/item_strfunc.cc
@@ -61,11 +61,6 @@ C_MODE_END
 
 size_t username_char_length= 16;
 
-/**
-   @todo Remove this. It is not safe to use a shared String object.
- */
-String my_empty_string("",default_charset_info);
-
 /*
   For the Items which have only val_str_ascii() method
   and don't have their own "native" val_str(),
@@ -103,7 +98,6 @@ String *Item_str_func::val_str_from_val_str_ascii(String *str, String *str2)
 }
 
 
-
 /*
   Convert an array of bytes to a hexadecimal representation.
 
@@ -2481,7 +2475,7 @@ String *Item_func_make_set::val_str(String *str)
   ulonglong bits;
   bool first_found=0;
   Item **ptr=args+1;
-  String *result=&my_empty_string;
+  String *result= make_empty_result();
 
   bits=args[0]->val_int();
   if ((null_value=args[0]->null_value))
diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h
index e0566b1d8c9..1731fcf7e99 100644
--- a/sql/item_strfunc.h
+++ b/sql/item_strfunc.h
@@ -1061,6 +1061,4 @@ public:
   String *val_str(String *);
 };
 
-extern String my_empty_string;
-
 #endif /* ITEM_STRFUNC_INCLUDED */
diff --git a/sql/sql_class.cc b/sql/sql_class.cc
index 732840c8d8d..2ead1b533d9 100644
--- a/sql/sql_class.cc
+++ b/sql/sql_class.cc
@@ -2284,6 +2284,7 @@ bool select_result::check_simple_select() const
 static String default_line_term("\n",default_charset_info);
 static String default_escaped("\\",default_charset_info);
 static String default_field_term("\t",default_charset_info);
+static String default_enclosed_and_line_start("", default_charset_info);
 static String default_xml_row_term("<row>", default_charset_info);
 
 sql_exchange::sql_exchange(char *name, bool flag,
@@ -2292,7 +2293,7 @@ sql_exchange::sql_exchange(char *name, bool flag,
 {
   filetype= filetype_arg;
   field_term= &default_field_term;
-  enclosed=   line_start= &my_empty_string;
+  enclosed=   line_start= &default_enclosed_and_line_start;
   line_term=  filetype == FILETYPE_CSV ?
               &default_line_term : &default_xml_row_term;
   escaped=    &default_escaped;