fix the NullPointerError of median (#50017)

python/paddle/fluid/tests/unittests/test_median.py

@@ -86,6 +86,7 @@ class TestMedian(unittest.TestCase):
         x = paddle.arange(12).reshape([3, 4])
         self.assertRaises(ValueError, paddle.median, x, 1.0)
         self.assertRaises(ValueError, paddle.median, x, 2)
+        self.assertRaises(ValueError, paddle.median, paddle.to_tensor([]))
 
 
 if __name__ == '__main__':

python/paddle/tensor/stat.py

@@ -406,6 +406,9 @@ def median(x, axis=None, keepdim=False, name=None):
     if not isinstance(x, Variable):
         raise TypeError("In median, the input x should be a Tensor.")
 
+    if x.size == 0:
+        raise ValueError("In median, the size of input x should not be 0.")
+
     if len(x.shape) == 0:
         return x.clone()