add whatsnew entry

Author: Jiang Yue

doc/source/whatsnew/v0.25.0.rst

@@ -133,6 +133,7 @@ Other Enhancements
 - :meth:`DataFrame.describe` now formats integer percentiles without decimal point (:issue:`26660`)
 - Added support for reading SPSS .sav files using :func:`read_spss` (:issue:`26537`)
 - Added new option ``plotting.backend`` to be able to select a plotting backend different than the existing ``matplotlib`` one. Use ``pandas.set_option('plotting.backend', '<backend-module>')`` where ``<backend-module`` is a library implementing the pandas plotting API (:issue:`14130`)
+- :meth:`io.json.json_normalize` now accepts a `fill_value` argument to fill NaN fields in given columns (:issue:`16918`)
 
 .. _whatsnew_0250.api_breaking:
 

pandas/tests/io/json/test_normalize.py

@@ -38,6 +38,7 @@ def deep_nested():
              }
             ]
 
+
 @pytest.fixture
 def deep_nested_missing():
     # deeply nested data with some missing values
@@ -65,6 +66,7 @@ def deep_nested_missing():
              }
             ]
 
+
 @pytest.fixture
 def state_data():
     return [