Throw exception on empty name of task, section or mark

src/main/kotlin/io/github/platan/tests_execution_chart/reporters/mermaid/core/MermaidGanttDiagram.kt

@@ -6,9 +6,23 @@ data class MermaidGanttDiagram(
     val entries: List<Entry>
 ) {
     sealed interface Entry
-    data class Section(val name: String) : Entry
-    data class Task(val name: String, val type: String?, val start: Long, val end: Long) : Entry
-    data class Milestone(val name: String, val timestamp: Long) : Entry
+    data class Section(val name: String) : Entry {
+        init {
+            require(name.isNotBlank()) { "Section name cannot be blank" }
+        }
+    }
+
+    data class Task(val name: String, val type: String?, val start: Long, val end: Long) : Entry {
+        init {
+            require(name.isNotBlank()) { "Task name cannot be blank" }
+        }
+    }
+
+    data class Milestone(val name: String, val timestamp: Long) : Entry {
+        init {
+            require(name.isNotBlank()) { "Mark name cannot be blank" }
+        }
+    }
 
     class MermaidGanttDiagramBuilder {
         private val entries: MutableList<Entry> = mutableListOf()

src/test/groovy/io/github/platan/tests_execution_chart/reporters/mermaid/core/MermaidGanttDiagramBuilderTest.groovy

@@ -0,0 +1,42 @@
+package io.github.platan.tests_execution_chart.reporters.mermaid.core
+
+import spock.lang.Specification
+
+class MermaidGanttDiagramBuilderTest extends Specification {
+
+    def "should return error for blank mark name"() {
+        when:
+        new MermaidGanttDiagram.MermaidGanttDiagramBuilder().addMilestone(name, 0)
+
+        then:
+        def e = thrown(IllegalArgumentException)
+        e.message == 'Mark name cannot be blank'
+
+        where:
+        name << ['', ' ']
+    }
+
+    def "should return error for blank task name"() {
+        when:
+        new MermaidGanttDiagram.MermaidGanttDiagramBuilder().addTask(name, 'active', 0, 1)
+
+        then:
+        def e = thrown(IllegalArgumentException)
+        e.message == 'Task name cannot be blank'
+
+        where:
+        name << ['', ' ']
+    }
+
+    def "should return error for blank section name"() {
+        when:
+        new MermaidGanttDiagram.MermaidGanttDiagramBuilder().addSection(name)
+
+        then:
+        def e = thrown(IllegalArgumentException)
+        e.message == 'Section name cannot be blank'
+
+        where:
+        name << ['', ' ']
+    }
+}