diff --git a/src/covjson_pydantic/ndarray.py b/src/covjson_pydantic/ndarray.py
index 1e065b7..6906335 100644
--- a/src/covjson_pydantic/ndarray.py
+++ b/src/covjson_pydantic/ndarray.py
@@ -23,7 +23,7 @@ class DataType(str, Enum):
 
 class NdArray(CovJsonBaseModel, Generic[NdArrayTypeT], extra="allow"):
     type: Literal["NdArray"] = "NdArray"
-    dataType: DataType = DataType.float  # noqa: N815
+    dataType: DataType  # noqa: N815
     axisNames: Optional[List[str]] = None  # noqa: N815
     shape: Optional[List[int]] = None
     values: List[Optional[NdArrayTypeT]] = None
@@ -31,6 +31,9 @@ class NdArray(CovJsonBaseModel, Generic[NdArrayTypeT], extra="allow"):
     @model_validator(mode="after")
     def check_data_type(self):
         t = typing.get_args(self.model_fields["values"].annotation)[0]
+        if t == typing.Optional[NdArrayTypeT]:
+            given_type = self.dataType.name if isinstance(self.dataType, DataType) else ""
+            raise ValueError(f"No NdArray type given, please specify as NdArray[{given_type}]")
         if self.dataType == DataType.float and not t == typing.Optional[float]:
             raise ValueError("dataType and NdArray type must both be float.")
         if self.dataType == DataType.str and not t == typing.Optional[str]:
diff --git a/tests/test_coverage.py b/tests/test_coverage.py
index 9f3a7cc..57447ce 100644
--- a/tests/test_coverage.py
+++ b/tests/test_coverage.py
@@ -69,6 +69,7 @@ def test_happy_cases(file_name, object_type):
     ("mixed-type-axes.json", Axes, r"Input should be a valid number"),
     ("mixed-type-axes-2.json", Axes, r"Input should be a valid string"),
     ("mixed-type-ndarray-1.json", NdArray[float], r"Input should be a valid number"),
+    ("mixed-type-ndarray-1.json", NdArray, r"No NdArray type given, please specify as NdArray\[float\]"),
     ("mixed-type-ndarray-2.json", NdArray[str], r"dataType and NdArray type must both be float"),
     ("mixed-type-ndarray-3.json", NdArray[int], r"Input should be a valid integer"),
     ("mixed-type-ndarray-3.json", NdArray[float], r"dataType and NdArray type must both be integer"),
diff --git a/tests/test_data/coverage-mixed-type-ndarray.json b/tests/test_data/coverage-mixed-type-ndarray.json
index 5bce9cb..41e6f5d 100644
--- a/tests/test_data/coverage-mixed-type-ndarray.json
+++ b/tests/test_data/coverage-mixed-type-ndarray.json
@@ -50,6 +50,14 @@
                     "en": "integer"
                 }
             }
+        },
+        "null-parameter": {
+            "type": "Parameter",
+            "observedProperty": {
+                "label": {
+                    "en": "null"
+                }
+            }
         }
     },
     "ranges": {
@@ -86,7 +94,7 @@
             ],
             "values": [
                 null,
-                62,
+                62.0,
                 63.136801411019825,
                 63.56289242989419,
                 63.98448554858814,
@@ -110,6 +118,24 @@
                 1,
                 2
             ]
+        },
+        "null-parameter": {
+            "type": "NdArray",
+            "dataType": "integer",
+            "axisNames": [
+                "x",
+                "y",
+                "t"
+            ],
+            "shape": [
+                1,
+                1,
+                2
+            ],
+            "values": [
+                null,
+                null
+            ]
         }
     },
     "extra:extra": "extra fields allowed"