Index: Riskeer/AssemblyTool/src/Riskeer.AssemblyTool.IO/Model/DataTypes/SerializableFailureMechanismSectionAssemblyResult.cs
===================================================================
diff -u -r9e9976818f1b446948c3bf815cafe2e023f98ac1 -rd82a2abacac1d8120c6e6119eae32092dd003802
--- Riskeer/AssemblyTool/src/Riskeer.AssemblyTool.IO/Model/DataTypes/SerializableFailureMechanismSectionAssemblyResult.cs	(.../SerializableFailureMechanismSectionAssemblyResult.cs)	(revision 9e9976818f1b446948c3bf815cafe2e023f98ac1)
+++ Riskeer/AssemblyTool/src/Riskeer.AssemblyTool.IO/Model/DataTypes/SerializableFailureMechanismSectionAssemblyResult.cs	(.../SerializableFailureMechanismSectionAssemblyResult.cs)	(revision d82a2abacac1d8120c6e6119eae32092dd003802)
@@ -46,7 +46,7 @@
         /// <param name="probability">The probability of this assembly result.</param>
         public SerializableFailureMechanismSectionAssemblyResult(SerializableAssemblyMethod assemblyMethod,
                                                                  SerializableFailureMechanismSectionAssemblyGroup assemblyGroup,
-                                                                 double? probability = null)
+                                                                 double probability)
             : this()
         {
             AssemblyMethod = assemblyMethod;
@@ -70,7 +70,7 @@
         /// Gets or sets the probability of this result.
         /// </summary>
         [XmlElement(AssemblyXmlIdentifiers.Probability)]
-        public double? Probability { get; set; }
+        public double Probability { get; set; }
 
         /// <summary>
         /// Gets or sets the status of this assembly result.
@@ -81,12 +81,12 @@
         /// <summary>
         /// Determines whether <see cref="Probability"/> should be serialized.
         /// </summary>
-        /// <returns><c>false</c> when <see cref="Probability"/> is <c>null</c>
-        /// or <see cref="AssemblyGroup"/> is <see cref="SerializableFailureMechanismSectionAssemblyGroup.NotDominant"/>;
+        /// <returns><c>false</c> when <see cref="AssemblyGroup"/> is
+        /// <see cref="SerializableFailureMechanismSectionAssemblyGroup.NotDominant"/>;
         /// <c>true</c> otherwise.</returns>
         public bool ShouldSerializeProbability()
         {
-            return Probability.HasValue && AssemblyGroup != SerializableFailureMechanismSectionAssemblyGroup.NotDominant;
+            return AssemblyGroup != SerializableFailureMechanismSectionAssemblyGroup.NotDominant;
         }
     }
 }
\ No newline at end of file
Index: Riskeer/AssemblyTool/test/Riskeer.AssemblyTool.IO.Test/Model/DataTypes/SerializableFailureMechanismSectionAssemblyResultTest.cs
===================================================================
diff -u -r9e9976818f1b446948c3bf815cafe2e023f98ac1 -rd82a2abacac1d8120c6e6119eae32092dd003802
--- Riskeer/AssemblyTool/test/Riskeer.AssemblyTool.IO.Test/Model/DataTypes/SerializableFailureMechanismSectionAssemblyResultTest.cs	(.../SerializableFailureMechanismSectionAssemblyResultTest.cs)	(revision 9e9976818f1b446948c3bf815cafe2e023f98ac1)
+++ Riskeer/AssemblyTool/test/Riskeer.AssemblyTool.IO.Test/Model/DataTypes/SerializableFailureMechanismSectionAssemblyResultTest.cs	(.../SerializableFailureMechanismSectionAssemblyResultTest.cs)	(revision d82a2abacac1d8120c6e6119eae32092dd003802)
@@ -40,7 +40,7 @@
             // Assert
             Assert.AreEqual((SerializableAssemblyMethod) 0, assemblyResult.AssemblyMethod);
             Assert.AreEqual((SerializableFailureMechanismSectionAssemblyGroup) 0, assemblyResult.AssemblyGroup);
-            Assert.IsNull(assemblyResult.Probability);
+            Assert.AreEqual(0, assemblyResult.Probability);
             Assert.AreEqual("VOLLDG", assemblyResult.Status);
 
             SerializableAttributeTestHelper.AssertXmlElementAttribute<SerializableFailureMechanismSectionAssemblyResult>(
@@ -116,21 +116,5 @@
             // Assert
             Assert.IsFalse(shouldSerialize);
         }
-
-        [Test]
-        public void ShouldSerializeProbability_WithoutProbability_ReturnsFalse()
-        {
-            // Setup
-            var random = new Random(39);
-            var assemblyResult = new SerializableFailureMechanismSectionAssemblyResult(
-                random.NextEnumValue<SerializableAssemblyMethod>(),
-                random.NextEnumValue<SerializableFailureMechanismSectionAssemblyGroup>());
-
-            // Call
-            bool shouldSerialize = assemblyResult.ShouldSerializeProbability();
-
-            // Assert
-            Assert.IsFalse(shouldSerialize);
-        }
     }
 }
\ No newline at end of file