kotlin-spring: fix exception thrown in enum.forValue

Author: swurzinger

modules/openapi-generator/src/main/resources/kotlin-spring/dataClass.mustache

@@ -39,7 +39,8 @@
             @JvmStatic
             @JsonCreator
             fun forValue(value: {{#isContainer}}{{#items}}{{{dataType}}}{{/items}}{{/isContainer}}{{^isContainer}}{{{dataType}}}{{/isContainer}}): {{{nameInPascalCase}}} {
-                return values().first{it -> it.value == value}
+                return values().firstOrNull{it -> it.value == value}
+                    ?: throw IllegalArgumentException("Unexpected value '$value' for enum '{{classname}}'")
             }
         }
     }

modules/openapi-generator/src/main/resources/kotlin-spring/enumClass.mustache

@@ -10,7 +10,8 @@ enum class {{classname}}(@get:JsonValue val value: {{dataType}}) {
         @JvmStatic
         @JsonCreator
         fun forValue(value: {{dataType}}): {{classname}} {
-                return values().first{it -> it.value == value}
+                return values().firstOrNull{it -> it.value == value}
+                    ?: throw IllegalArgumentException("Unexpected value '$value' for enum '{{classname}}'")
         }
     }
 }