Fixed #25580 -- Allowed `None` to be set as SRID value.

django/contrib/gis/geos/geometry.py

@@ -366,7 +366,7 @@ class GEOSGeometry(GEOSBase, ListMixin):
 
     def set_srid(self, srid):
         "Sets the SRID for the geometry."
-        capi.geos_set_srid(self.ptr, srid)
+        capi.geos_set_srid(self.ptr, 0 if srid is None else srid)
     srid = property(get_srid, set_srid)
 
     # #### Output Routines ####

tests/gis_tests/geos_tests/test_geos.py

@@ -650,6 +650,10 @@ class GEOSTest(unittest.TestCase, TestDataMixin):
         p3 = fromstr(p1.hex, srid=-1)  # -1 is intended.
         self.assertEqual(-1, p3.srid)
 
+        # Testing that geometry SRID could be set to its own value
+        pnt_wo_srid = Point(1, 1)
+        pnt_wo_srid.srid = pnt_wo_srid.srid
+
     @skipUnless(HAS_GDAL, "GDAL is required.")
     def test_custom_srid(self):
         """ Test with a srid unknown from GDAL """