diff --git a/src/openeo_grass_gis_driver/actinia_processing/mask_polygon_process.py b/src/openeo_grass_gis_driver/actinia_processing/mask_polygon_process.py
index 650ff8f..3d78a54 100644
--- a/src/openeo_grass_gis_driver/actinia_processing/mask_polygon_process.py
+++ b/src/openeo_grass_gis_driver/actinia_processing/mask_polygon_process.py
@@ -48,7 +48,7 @@ def create_process_description():
     )
     p_value = Parameter(
         description="The value used to replace non-zero and `true` values with",
-        schema={"type": "object", "subtype": "string"},
+        schema={"type": ["number", "boolean", "string", "null"]},
         optional=True,
     )
     p_inside = Parameter(
diff --git a/src/openeo_grass_gis_driver/actinia_processing/mask_process.py b/src/openeo_grass_gis_driver/actinia_processing/mask_process.py
index d9f1890..5a9c63c 100644
--- a/src/openeo_grass_gis_driver/actinia_processing/mask_process.py
+++ b/src/openeo_grass_gis_driver/actinia_processing/mask_process.py
@@ -3,14 +3,23 @@
 from random import randint
 from typing import Tuple
 
-from openeo_grass_gis_driver.models.process_graph_schemas import \
-     ProcessGraphNode, ProcessGraph
-
-from openeo_grass_gis_driver.actinia_processing.base import \
-     check_node_parents, DataObject, GrassDataType, \
-     create_output_name
-from openeo_grass_gis_driver.models.process_schemas import \
-     Parameter, ProcessDescription, ReturnValue, ProcessExample
+from openeo_grass_gis_driver.models.process_graph_schemas import (
+    ProcessGraphNode,
+    ProcessGraph,
+)
+
+from openeo_grass_gis_driver.actinia_processing.base import (
+    check_node_parents,
+    DataObject,
+    GrassDataType,
+    create_output_name,
+)
+from openeo_grass_gis_driver.models.process_schemas import (
+    Parameter,
+    ProcessDescription,
+    ReturnValue,
+    ProcessExample,
+)
 from .base import PROCESS_DICT, PROCESS_DESCRIPTION_DICT, Node
 
 __license__ = "Apache License, Version 2.0"
@@ -26,26 +35,25 @@ def create_process_description():
     p_data = Parameter(
         description="Any openEO process object that returns raster datasets "
         "or space-time raster dataset",
-        schema={
-            "type": "object",
-            "subtype": "raster-cube"},
-        optional=False)
+        schema={"type": "object", "subtype": "raster-cube"},
+        optional=False,
+    )
     p_mask = Parameter(
         description="Any openEO process object that returns raster datasets "
         "or space-time raster dataset",
-        schema={
-            "type": "object",
-            "subtype": "raster-cube"},
-        optional=False)
+        schema={"type": "object", "subtype": "raster-cube"},
+        optional=False,
+    )
     p_value = Parameter(
         description="The value used to replace non-zero and `true` values with",
-        schema={
-            "type": "object",
-            "subtype": "string"},
-        optional=True)
+        schema={"type": ["number", "boolean", "string", "null"]},
+        optional=True,
+    )
 
-    rv = ReturnValue(description="Processed EO data.",
-                     schema={"type": "object", "subtype": "raster-cube"})
+    rv = ReturnValue(
+        description="Processed EO data.",
+        schema={"type": "object", "subtype": "raster-cube"},
+    )
 
     # Example
     arguments = {
@@ -55,27 +63,23 @@ def create_process_description():
     }
     node = ProcessGraphNode(process_id=PROCESS_NAME, arguments=arguments)
     graph = ProcessGraph(
-        title="title",
-        description="description",
-        process_graph={
-            "mask_1": node})
+        title="title", description="description", process_graph={"mask_1": node}
+    )
     examples = [
         ProcessExample(
-            title="Simple example",
-            description="Simple example",
-            process_graph=graph)]
+            title="Simple example", description="Simple example", process_graph=graph
+        )
+    ]
 
     pd = ProcessDescription(
         id=PROCESS_NAME,
         description="Applies a mask to a raster data cube "
         " replacing pixels in data that are not null in mask with the new value.",
         summary="Applies a mask to a raster data cube",
-        parameters={
-            "data": p_data,
-            "mask": p_mask,
-            "replacement": p_value},
+        parameters={"data": p_data, "mask": p_mask, "replacement": p_value},
         returns=rv,
-        examples=[examples])
+        examples=[examples],
+    )
 
     return json.loads(pd.to_json())
 
@@ -84,10 +88,11 @@ def create_process_description():
 
 
 def create_process_chain_entry(
-        input_object: DataObject,
-        mask_object: DataObject,
-        mask_value: str,
-        output_object: DataObject):
+    input_object: DataObject,
+    mask_object: DataObject,
+    mask_value: str,
+    output_object: DataObject,
+):
     """Create a Actinia command of the process chain that uses t.rast.mapcalc
     to mask raster values based on a mask dataset and a replacement value
 
@@ -105,27 +110,30 @@ def create_process_chain_entry(
 
     pc = []
 
-    p = {"id": "t_rast_mask_%i" % rn,
-         "module": "t.rast.mask",
-         "inputs": [{"param": "input",
-                     "value": input_object.grass_name()},
-                    {"param": "mask",
-                     "value": mask_object.grass_name()},
-                    {"param": "basename",
-                     "value": output_object.name},
-                    {"param": "output",
-                     "value": output_object.grass_name()},
-                    {"param": "value",
-                     "value": mask_value}],
-         "flags": "i"}
+    p = {
+        "id": "t_rast_mask_%i" % rn,
+        "module": "t.rast.mask",
+        "inputs": [
+            {"param": "input", "value": input_object.grass_name()},
+            {"param": "mask", "value": mask_object.grass_name()},
+            {"param": "basename", "value": output_object.name},
+            {"param": "output", "value": output_object.grass_name()},
+            {"param": "value", "value": mask_value},
+        ],
+        "flags": "i",
+    }
 
     pc.append(p)
 
-    p = {"id": "t_info_%i" % rn,
-         "module": "t.info",
-         "inputs": [{"param": "input", "value": output_object.grass_name()},
-                    {"param": "type", "value": "strds"}],
-         "flags": 'g'}
+    p = {
+        "id": "t_info_%i" % rn,
+        "module": "t.info",
+        "inputs": [
+            {"param": "input", "value": output_object.grass_name()},
+            {"param": "type", "value": "strds"},
+        ],
+        "flags": "g",
+    }
 
     pc.append(p)
 
@@ -142,11 +150,8 @@ def get_process_list(node: Node) -> Tuple[list, list]:
     input_objects, process_list = check_node_parents(node=node)
     output_objects = []
 
-    if "data" not in node.arguments or \
-            "mask" not in node.arguments:
-        raise Exception(
-            "Process %s requires parameter data, mask" %
-            PROCESS_NAME)
+    if "data" not in node.arguments or "mask" not in node.arguments:
+        raise Exception("Process %s requires parameter data, mask" % PROCESS_NAME)
 
     if "replacement" in node.arguments:
         mask_value = node.arguments["replacement"]
@@ -154,24 +159,16 @@ def get_process_list(node: Node) -> Tuple[list, list]:
         mask_value = "null"
 
     # Get the input and mask data separately
-    data_object = list(
-        node.get_parent_by_name(
-            parent_name="data").output_objects)[0]
-    mask_object = list(
-        node.get_parent_by_name(
-            parent_name="mask").output_objects)[0]
+    data_object = list(node.get_parent_by_name(parent_name="data").output_objects)[0]
+    mask_object = list(node.get_parent_by_name(parent_name="mask").output_objects)[0]
 
     output_object = DataObject(
-        name=create_output_name(data_object.name, node),
-        datatype=GrassDataType.STRDS)
+        name=create_output_name(data_object.name, node), datatype=GrassDataType.STRDS
+    )
     output_objects.append(output_object)
     node.add_output(output_object=output_object)
 
-    pc = create_process_chain_entry(
-        data_object,
-        mask_object,
-        mask_value,
-        output_object)
+    pc = create_process_chain_entry(data_object, mask_object, mask_value, output_object)
     process_list.extend(pc)
 
     return output_objects, process_list