change default value of explode attribute to None; (#18)

Author: Gamazic

pydantic_openapi_schema/v3_1_0/parameter.py

@@ -78,7 +78,7 @@ class Parameter(BaseModel):
     - for `cookie` - `form`.
     """
 
-    explode: bool = False
+    explode: Optional[bool] = None
     """When this is true, parameter values of type `array` or `object` generate
     separate parameters for each value of the array or key-value pair of the
     map.