Error in @: no applicable method for @ applied to an object of class "NULL"

[DaiZYlab]

Azimuth::AzimuthApp(reference = '~/R/Kala/ref')

Listening on http://127.0.0.1:5470
Warning: Overwriting miscellanous data for model
Warning: Adding a dimensional reduction (refUMAP) without the associated assay being present
Warning: Adding a dimensional reduction (refUMAP) without the associated assay being present
[1] "resetting..."
detected inputs from HUMAN with id type Gene.name
reference rownames detected HUMAN with id type Gene.name
Warning: Removed 1 row containing missing values or values outside the scale range (geom_hline()).
Warning: Removed 1 row containing missing values or values outside the scale range (geom_rect()).
Warning: Removed 1 row containing missing values or values outside the scale range (geom_hline()).
Warning: Removed 1 row containing missing values or values outside the scale range (geom_hline()).
Warning: Removed 1 row containing missing values or values outside the scale range (geom_rect()).
Warning: Removed 1 row containing missing values or values outside the scale range (geom_rect()).
Running SCTransform on assay: RNA
Running SCTransform on layer: counts
Using reference SCTModel to calculate pearson residuals
Determine variable features
Setting min_variance to: -Inf
Calculating residuals of type pearson for 4870 genes
|=======================================================================================================================================| 100%
|=======================================================================================================================================| 100%
Getting residuals for block 1(of 3) for counts dataset
Getting residuals for block 2(of 3) for counts dataset
Getting residuals for block 3(of 3) for counts dataset
|=======================================================================================================================================| 100%
Finished calculating residuals for counts
Set default assay to refAssay
Warning: 130 features of the features specified were not present in both the reference query assays.
Continuing with remaining 4870 features.
Projecting cell embeddings
Finding query neighbors
Finding neighborhoods
Finding anchors
Found 6163 anchors
Finding integration vectors
Finding integration vector weights
0% 10 20 30 40 50 60 70 80 90 100%
[----|----|----|----|----|----|----|----|----|----|
**************************************************|
Predicting cell labels
| | 0 % ~calculating
Integrating dataset 2 with reference dataset
Finding integration vectors
Integrating data
|++++++++++++++++++++++++++++++++++++++++++++++++++| 100% elapsed=01s
Warning: Keys should be one or more alphanumeric characters followed by an underscore, setting key from integrated_dr_ to integrateddr_
Warning: Error in @: no applicable method for @ applied to an object of class "NULL"

I use Seurat v5.1 offline for the Azimuth. The error message is shown above. Anyone knows how to fix it?