ENH: generate_label_classes_crop_centers: warn only if ratio of missi…

…ng class is not set to 0

monai/transforms/utils.py

@@ -625,9 +625,12 @@ def generate_label_classes_crop_centers(
 
     for i, array in enumerate(indices):
         if len(array) == 0:
-            ratios_[i] = 0
-            if warn:
-                warnings.warn(f"no available indices of class {i} to crop, set the crop ratio of this class to zero.")
+            if ratios_[i] != 0:
+                ratios_[i] = 0
+                if warn:
+                    warnings.warn(
+                        f"no available indices of class {i} to crop, set the crop ratio of this class to zero."
+                    )
 
     centers = []
     classes = rand_state.choice(len(ratios_), size=num_samples, p=np.asarray(ratios_) / np.sum(ratios_))