Add type hints

Author: MDUYN

README.md

@@ -45,6 +45,9 @@ Indicators that help to determine the direction of the market (uptrend, downtren
 
 #### Weighted Moving Average (WMA)
 
+```python
+def wma(data: Union[PdDataFrame, PlDataFrame], source_column: str, period: int, result_column: Optional[str] = None) -> Union[PdDataFrame, PlDataFrame]
+
 ```python
 from investing_algorithm_framework import CSVOHLCVMarketDataSource
 

pyindicators/indicators/weighted_moving_average.py

@@ -1,4 +1,4 @@
-from typing import Union
+from typing import Union, Optional
 
 import numpy as np
 from pandas import DataFrame as PdDataFrame
@@ -13,7 +13,7 @@ def wma(
     data: Union[PdDataFrame, PlDataFrame],
     source_column: str,
     period: int,
-    result_column: str = None,
+    result_column: Optional[str] = None,
 ) -> Union[PdDataFrame, PlDataFrame]:
     """
     Function to calculate the weighted moving average of a series.