fix(data_frame): parsing empty query result value as numpy.NaN (#584)

Author: bednar

CHANGELOG.md

@@ -2,7 +2,7 @@
 
 ### Breaking Changes
 
-This release disables using of the HTTP proxy environment variables `HTTP_PROXY` and `HTTPS_PROXY` for the asynchronous HTTP client. 
+This release disables using of the HTTP proxy environment variables `HTTP_PROXY` and `HTTPS_PROXY` for the asynchronous HTTP client.
 The proxy environment variables must be explicitly enabled in the client's configuration:
 
 ```python
@@ -15,6 +15,7 @@ async with InfluxDBClientAsync(url="http://localhost:8086", token="my-token", or
 
 ### Bug Fixes
 1. [#583](https://github.com/influxdata/influxdb-client-python/pull/583): Async HTTP client doesn't always use `HTTP_PROXY`/`HTTPS_PROXY` environment variables. [async/await]
+1. [#584](https://github.com/influxdata/influxdb-client-python/pull/584): Parsing empty query result value as `numpy.NaN`
 
 ## 1.36.1 [2023-02-23]
 

influxdb_client/client/flux_csv_parser.py

@@ -272,6 +272,9 @@ def _to_value(self, str_val, column):
         if str_val == '' or str_val is None:
             default_value = column.default_value
             if default_value == '' or default_value is None:
+                if self._serialization_mode is FluxSerializationMode.dataFrame:
+                    from ..extras import np
+                    return self._to_value(np.nan, column)
                 return None
             return self._to_value(default_value, column)
 

tests/test_FluxCSVParser.py

@@ -263,6 +263,19 @@ def test_pandas_column_datatype(self):
         self.assertEqual('bool', df.dtypes['value4'].name)
         self.assertEqual('float64', df.dtypes['value5'].name)
 
+    def test_pandas_null_bool_types(self):
+        data = "#datatype,string,long,dateTime:RFC3339,dateTime:RFC3339,string,string,string,string,boolean\n" \
+               "#group,false,false,true,true,true,true,true,true,false\n" \
+               "#default,_result,,,,,,,,\n" \
+               ",result,table,_start,_stop,_field,_measurement,host,region,value\n" \
+               ",,0,1977-09-21T00:12:43.145224192Z,2018-07-16T11:21:02.547596934Z,free,mem,A,west,true\n" \
+               ",,0,1977-09-21T00:12:43.145224192Z,2018-07-16T11:21:02.547596934Z,free,mem,A,west,\n"
+
+        parser = self._parse(data=data, serialization_mode=FluxSerializationMode.dataFrame,
+                             response_metadata_mode=FluxResponseMetadataMode.full)
+        df = list(parser.generator())[0]
+        self.assertEqual('bool', df.dtypes['value'].name)
+
     def test_parse_without_datatype(self):
         data = ",result,table,_start,_stop,_field,_measurement,host,region,_value2,value1,value_str\n" \
                ",,0,1677-09-21T00:12:43.145224192Z,2018-07-16T11:21:02.547596934Z,free,mem,A,west,121,11,test\n" \