Handle submitting form without csp estimate

atst/models/task_order.py

@@ -88,7 +88,7 @@ class TaskOrder(Base, mixins.TimestampsMixin):
             )
         elif not new_csp_estimate and self._csp_estimate:
             self._csp_estimate = None
-        else:
+        elif new_csp_estimate:
             raise TypeError("Could not set csp_estimate with invalid type")
 
     @property

tests/models/test_task_order.py

@@ -59,6 +59,13 @@ class TestCSPEstimate:
         with pytest.raises(TypeError):
             to.csp_estimate = "invalid"
 
+    def test_setting_estimate_with_empty_value(self):
+        to = TaskOrder()
+        assert to.csp_estimate is None
+
+        to.csp_estimate = ""
+        assert to.csp_estimate is None
+
     def test_removing_estimate(self):
         attachment = Attachment(filename="sample.pdf", object_name="sample")
         to = TaskOrder(csp_estimate=attachment)