Refs #35074 -- Avoided failed attempts to remove spatial indexes on nullable fields on MySQL.

MySQL doesn't support spatial indexes on NULL columns, so there is no
point in removing them.

django/contrib/gis/db/backends/mysql/schema.py

@@ -54,7 +54,7 @@ class MySQLGISSchemaEditor(DatabaseSchemaEditor):
         self.create_spatial_indexes()
 
     def remove_field(self, model, field):
-        if isinstance(field, GeometryField) and field.spatial_index:
+        if isinstance(field, GeometryField) and field.spatial_index and not field.null:
             index_name = self._create_spatial_index_name(model, field)
             sql = self._delete_index_sql(model, index_name)
             try:

tests/gis_tests/gis_migrations/test_operations.py

@@ -133,6 +133,24 @@ class OperationTests(OperationTestCase):
         if self.has_spatial_indexes:
             self.assertSpatialIndexExists("gis_neighborhood", "path")
 
+    @skipUnless(connection.vendor == "mysql", "MySQL specific test")
+    def test_remove_geom_field_nullable_with_index(self):
+        # MySQL doesn't support spatial indexes on NULL columns.
+        with self.assertNumQueries(1) as ctx:
+            self.alter_gis_model(
+                migrations.AddField,
+                "Neighborhood",
+                "path",
+                fields.LineStringField,
+                field_class_kwargs={"null": True},
+            )
+        self.assertColumnExists("gis_neighborhood", "path")
+        self.assertNotIn("CREATE SPATIAL INDEX", ctx.captured_queries[0]["sql"])
+
+        with self.assertNumQueries(1), self.assertNoLogs("django.contrib.gis", "ERROR"):
+            self.alter_gis_model(migrations.RemoveField, "Neighborhood", "path")
+        self.assertColumnNotExists("gis_neighborhood", "path")
+
     @skipUnless(HAS_GEOMETRY_COLUMNS, "Backend doesn't support GeometryColumns.")
     def test_geom_col_name(self):
         self.assertEqual(