Backport PR #1667: Fix/nan datetimes in url (#1667)

* fix: NaN datetimes in url upon refresh

Signed-off-by: F.N. Claessen <felix@seita.nl>

* Revert "fix: NaN datetimes in url upon refresh"

This reverts commit cdbe0ee.

* fix: NaN datetimes in url upon refresh, but keep human-friendly datetime format in url

Signed-off-by: F.N. Claessen <felix@seita.nl>

* docs: add inline explanation

Signed-off-by: F.N. Claessen <felix@seita.nl>

* docs: changelog entry

Signed-off-by: F.N. Claessen <felix@seita.nl>

* docs: touch up previous changelog entry

Signed-off-by: F.N. Claessen <felix@seita.nl>

* docs: add release date for v0.27.3

Signed-off-by: F.N. Claessen <felix@seita.nl>

* fix: in case of None values

Signed-off-by: F.N. Claessen <felix@seita.nl>

* refactor: simplify using loop

Signed-off-by: F.N. Claessen <felix@seita.nl>

---------

Signed-off-by: F.N. Claessen <felix@seita.nl>
(cherry picked from commit ad8b9dc)

Author: Flix6x

documentation/changelog.rst

@@ -25,11 +25,12 @@ Bugfixes
 * Fixed usage of slow query for status page [see `PR #1638 <https://www.github.com/FlexMeasures/flexmeasures/pull/1638>`_]
 
 
-v0.27.3 | August XX, 2025
+v0.27.3 | August 19, 2025
 ============================
 
 Bugfixes
 -----------
+* Fix the time window in the UI from being replaced with :abbr:`NaN (not a number)` values when refreshing the asset graphs page [see `PR #1667 <https://github.com/FlexMeasures/flexmeasures/pull/1667>`_]
 * Fix scheduling storage devices within a single time step [see `PR #1619 <https://github.com/FlexMeasures/flexmeasures/pull/1619>`_]
 
 
@@ -38,7 +39,7 @@ v0.27.2 | August 13, 2025
 
 Bugfixes
 -----------
-* Resolve issue where concatenating sensor data from updated reporters leads to a NaN source and crashing the asset chart page [see `PR #1660 <https://github.com/FlexMeasures/flexmeasures/pull/1660>`_]
+* Resolve issue where concatenating sensor data from updated reporters leads to a :abbr:`NaN (not a number)` source and crashing the asset graphs page [see `PR #1660 <https://github.com/FlexMeasures/flexmeasures/pull/1660>`_]
 
 Infrastructure / Support
 ----------------------

flexmeasures/ui/utils/view_utils.py

@@ -55,13 +55,13 @@ def render_flexmeasures_template(html_filename: str, **variables):
     ):
         variables["documentation_exists"] = True
 
-    # use event_starts_after and event_ends_before from session if not given
-    variables["event_starts_after"] = variables.get(
-        "event_starts_after"
-    ) or session.get("event_starts_after")
-    variables["event_ends_before"] = variables.get("event_ends_before") or session.get(
-        "event_ends_before"
-    )
+    # Use event_starts_after and event_ends_before from session if not given
+    # and resolve url encoding issue for timezone offsets with plus sign
+    for key in ["event_starts_after", "event_ends_before"]:
+        value = variables.get(key) or session.get(key)
+        if isinstance(value, str):
+            value = value.replace(" ", "+")
+        variables[key] = value
 
     variables["chart_type"] = session.get("chart_type", "bar_chart")