Only import the jinja2 instrumentation when jinja2 itself is importab…

…le (#1954)

Closes #1949.

debug_toolbar/panels/templates/panel.py

@@ -1,4 +1,5 @@
 from contextlib import contextmanager
+from importlib.util import find_spec
 from os.path import normpath
 from pprint import pformat, saferepr
 
@@ -14,7 +15,11 @@
 from debug_toolbar.panels import Panel
 from debug_toolbar.panels.sql.tracking import SQLQueryTriggered, allow_sql
 from debug_toolbar.panels.templates import views
-from debug_toolbar.panels.templates.jinja2 import patch_jinja_render
+
+if find_spec("jinja2"):
+    from debug_toolbar.panels.templates.jinja2 import patch_jinja_render
+
+    patch_jinja_render()
 
 # Monkey-patch to enable the template_rendered signal. The receiver returns
 # immediately when the panel is disabled to keep the overhead small.
@@ -26,8 +31,6 @@
     Template.original_render = Template._render
     Template._render = instrumented_test_render
 
-patch_jinja_render()
-
 # Monkey-patch to store items added by template context processors. The
 # overhead is sufficiently small to justify enabling it unconditionally.