diff --git a/hsmodels/schemas/fields.py b/hsmodels/schemas/fields.py
index 1732011..be9d05b 100644
--- a/hsmodels/schemas/fields.py
+++ b/hsmodels/schemas/fields.py
@@ -974,5 +974,5 @@ class AdditionalMetadata(BaseMetadata):
     class Config:
         title = "Additional metadata"
 
-    key: str = Field(title="Key", description="A string for the additional metadata key")
-    value: str = Field(title="Value", description="A string for the additional metadata value")
+    key: str = Field(title="Key", description="A string for the additional metadata key", default="")
+    value: str = Field(title="Value", description="A string for the additional metadata value", default="")
diff --git a/setup.py b/setup.py
index 8713b08..8cc3ab8 100644
--- a/setup.py
+++ b/setup.py
@@ -4,7 +4,7 @@
 
 setup(
     name='hsmodels',
-    version='0.3.5',
+    version='0.3.6',
     packages=find_packages(include=['hsmodels', 'hsmodels.*', 'hsmodels.schemas.*', 'hsmodels.schemas.rdf.*'],
                            exclude=("tests",)),
     install_requires=[