diff --git a/brewman/alembic/versions/48af31eb6f3f_fp.py b/brewman/alembic/versions/48af31eb6f3f_fp.py
new file mode 100644
index 00000000..eafa00e4
--- /dev/null
+++ b/brewman/alembic/versions/48af31eb6f3f_fp.py
@@ -0,0 +1,24 @@
+"""FP
+
+Revision ID: 48af31eb6f3f
+Revises: 12262aadbc08
+Create Date: 2023-08-07 13:01:05.401492
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision = '48af31eb6f3f'
+down_revision = '12262aadbc08'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.create_unique_constraint(op.f('uq_fingerprints_date'), 'fingerprints', ['date', 'employee_id'])
+
+
+def downgrade():
+    op.drop_constraint(op.f('uq_fingerprints_date'), 'fingerprints', type_='unique')
diff --git a/brewman/brewman/models/fingerprint.py b/brewman/brewman/models/fingerprint.py
index 6f235bc2..9184e425 100644
--- a/brewman/brewman/models/fingerprint.py
+++ b/brewman/brewman/models/fingerprint.py
@@ -3,7 +3,7 @@ import uuid
 from datetime import datetime
 from typing import TYPE_CHECKING
 
-from sqlalchemy import DateTime, ForeignKey, Uuid
+from sqlalchemy import DateTime, ForeignKey, UniqueConstraint, Uuid
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from ..db.base_class import reg
@@ -16,6 +16,7 @@ if TYPE_CHECKING:
 @reg.mapped_as_dataclass(unsafe_hash=True)
 class Fingerprint:
     __tablename__ = "fingerprints"
+    __table_args__ = (UniqueConstraint("date", "employee_id"),)
 
     id: Mapped[uuid.UUID] = mapped_column(Uuid, primary_key=True, insert_default=uuid.uuid4)
     employee_id: Mapped[uuid.UUID] = mapped_column(Uuid, ForeignKey("employees.id"), nullable=False)
diff --git a/brewman/brewman/schemas/client.py b/brewman/brewman/schemas/client.py
index f09b7d27..7d8076c4 100644
--- a/brewman/brewman/schemas/client.py
+++ b/brewman/brewman/schemas/client.py
@@ -44,11 +44,13 @@ class ClientList(Client):
 
     @field_validator("last_date", mode="before")
     @classmethod
-    def parse_last_date(cls, value: datetime | str) -> datetime | None:
+    def parse_last_date(cls, value: datetime | str | None) -> datetime | None:
+        if value is None or value == "":
+            return None
         if isinstance(value, datetime):
             return value
         return datetime.strptime(value, "%d-%b-%Y %H:%M")
 
     @field_serializer("last_date")
-    def serialize_last_date(self, value: datetime, info: FieldSerializationInfo) -> str:
-        return value.strftime("%d-%b-%Y %H:%M")
+    def serialize_last_date(self, value: datetime | None, info: FieldSerializationInfo) -> str | None:
+        return None if value is None else value.strftime("%d-%b-%Y %H:%M")