[libgda/LIBGDA_5.2] Time/Date/Timestamp: return NULL string if no set

[Daniel Espinosa Ortiz <despinosa src gnome org>]

commit d308f5bad9db134f0f8b68662bf5ec9601f2b7ee
Author: Daniel Espinosa <esodan gmail com>
Date:   Mon Apr 22 17:44:03 2019 -0500

    Time/Date/Timestamp: return NULL string if no set

 NEWS               |  1 +
 libgda/gda-value.c | 15 ++++++++++-----
 2 files changed, 11 insertions(+), 5 deletions(-)
---
diff --git a/NEWS b/NEWS
index eab8243c3..41bc53dff 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,7 @@ libgda 5.2.9
  - Fix Sun JRE 1.8 detection
  - Drop unneeded JAVAH variable check
  - Fix build for System Installed SQLite libs
+ - Non-Dates and Timestamps values returns 'NULL' string when converted
 
 libgda 5.2.8 2018-12-03
  - Fix a typo on sv translation
diff --git a/libgda/gda-value.c b/libgda/gda-value.c
index 795a11ef4..7ad7dcfad 100644
--- a/libgda/gda-value.c
+++ b/libgda/gda-value.c
@@ -727,7 +727,7 @@ numeric_to_string (const GValue *src, GValue *dest)
        if (numeric)
                g_value_set_string (dest, numeric->number);
        else
-               g_value_set_string (dest, "0.0");
+               g_value_set_string (dest, "NULL");
 }
 
 static void
@@ -1080,7 +1080,7 @@ time_to_string (const GValue *src, GValue *dest)
                g_string_free (string, FALSE);
        }
        else
-               g_value_set_string (dest, "00:00:00");
+               g_value_set_string (dest, "NULL");
 }
 
 /* Transform a String GValue to a GdaTime from a string like "12:30:15+01" */
@@ -2341,8 +2341,13 @@ gda_value_stringify (const GValue *value)
                g_ascii_formatd (buffer, sizeof (buffer), "%f", g_value_get_double (value));
                return g_strdup (buffer);
        }
-       else if (type == GDA_TYPE_NUMERIC)
-               return gda_numeric_get_string (gda_value_get_numeric (value));
+       else if (type == GDA_TYPE_NUMERIC) {
+               gchar *str = gda_numeric_get_string (gda_value_get_numeric (value));
+    if (str == NULL) {
+      str = g_strdup ("NULL");
+    }
+    return str;
+  }
        else if (type == G_TYPE_DATE) {
                GDate *date;
                date = (GDate *) g_value_get_boxed (value);
@@ -2357,7 +2362,7 @@ gda_value_stringify (const GValue *value)
                                                        date->year, date->month, date->day);
                }
                else
-                       return g_strdup ("0000-00-00");
+                       return g_strdup ("NULL");
        }
        else if (g_value_type_transformable (G_VALUE_TYPE (value), G_TYPE_STRING)) {
                GValue *string;