chore: address PR feedback

Author: MaggieKimani1

src/Microsoft.OpenApi/Extensions/OpenApiTypeMapper.cs

@@ -49,6 +49,17 @@ public static string[] ToIdentifier(this JsonSchemaType schemaType)
             return types.ToArray();
         }
 
+        /// <summary>
+        /// Returns the first identifier from a string array.
+        /// </summary>
+        /// <param name="schemaType"></param>
+        /// <returns></returns>
+        public static string FirstIdentifier(this JsonSchemaType schemaType)
+        {
+            var identifier = schemaType.ToIdentifier();
+            return identifier[0];
+        }
+
 #nullable restore
 
         /// <summary>
@@ -77,8 +88,13 @@ public static JsonSchemaType ToJsonSchemaType(this string identifier)
         /// </summary>
         /// <param name="identifier"></param>
         /// <returns></returns>
-        public static JsonSchemaType ToJsonSchemaType(this string[] identifier)
+        public static JsonSchemaType? ToJsonSchemaType(this string[] identifier)
         {
+            if (identifier == null)
+            {
+                return null;
+            }
+
             JsonSchemaType type = 0;
             foreach (var id in identifier)
             {
@@ -170,7 +186,7 @@ public static Type MapOpenApiPrimitiveTypeToSimpleType(this OpenApiSchema schema
                 throw new ArgumentNullException(nameof(schema));
             }
             var isNullable = (schema.Type & JsonSchemaType.Null) == JsonSchemaType.Null;
-            var nonNullable = (schema.Type & ~JsonSchemaType.Null).ToIdentifier().FirstOrDefault();
+            var nonNullable = (schema.Type & ~JsonSchemaType.Null)?.FirstIdentifier();
 
             var type = (nonNullable, schema.Format?.ToLowerInvariant(), isNullable) switch
             {

src/Microsoft.OpenApi/Models/OpenApiSchema.cs

@@ -413,7 +413,7 @@ internal void WriteJsonSchemaKeywords(IOpenApiWriter writer)
         internal void WriteAsItemsProperties(IOpenApiWriter writer)
         {
             // type
-            writer.WriteProperty(OpenApiConstants.Type, (Type & ~JsonSchemaType.Null).ToIdentifier()?.FirstOrDefault());
+            writer.WriteProperty(OpenApiConstants.Type, (Type & ~JsonSchemaType.Null)?.FirstIdentifier());
 
             // format
             WriteFormatProperty(writer);
@@ -651,14 +651,14 @@ Extensions is not null &&
                         break;
                     case OpenApiSpecVersion.OpenApi3_0 when isNullable && type.Value == JsonSchemaType.Null:
                         writer.WriteProperty(OpenApiConstants.Nullable, true);
-                        writer.WriteProperty(OpenApiConstants.Type, JsonSchemaType.Object.ToIdentifier().FirstOrDefault());
+                        writer.WriteProperty(OpenApiConstants.Type, JsonSchemaType.Object.FirstIdentifier());
                         break;
                     case OpenApiSpecVersion.OpenApi3_0 when isNullable && type.Value != JsonSchemaType.Null:
                         writer.WriteProperty(OpenApiConstants.Nullable, true);
-                        writer.WriteProperty(OpenApiConstants.Type, type.Value.ToIdentifier().FirstOrDefault());
+                        writer.WriteProperty(OpenApiConstants.Type, type.Value.FirstIdentifier());
                         break;
                     default:
-                        writer.WriteProperty(OpenApiConstants.Type, type.Value.ToIdentifier().FirstOrDefault());
+                        writer.WriteProperty(OpenApiConstants.Type, type.Value.FirstIdentifier());
                         break;
                 }
             }
@@ -703,7 +703,7 @@ private static void UpCastSchemaTypeToV31(JsonSchemaType type, IOpenApiWriter wr
             var temporaryType = type | JsonSchemaType.Null;
             var list = (from JsonSchemaType flag in jsonSchemaTypeValues// Check if the flag is set in 'type' using a bitwise AND operation
                         where temporaryType.HasFlag(flag)
-                        select flag.ToIdentifier().FirstOrDefault()).ToList();
+                        select flag.FirstIdentifier()).ToList();
             if (list.Count > 1)
             {
                 writer.WriteOptionalCollection(OpenApiConstants.Type, list, (w, s) => w.WriteValue(s));
@@ -740,7 +740,7 @@ private void DowncastTypeArrayToV2OrV3(JsonSchemaType schemaType, IOpenApiWriter
                     if (schemaType.HasFlag(flag) && flag != JsonSchemaType.Null)
                     {
                         // Write the non-null flag value to the writer
-                        writer.WriteProperty(OpenApiConstants.Type, flag.ToIdentifier().FirstOrDefault());
+                        writer.WriteProperty(OpenApiConstants.Type, flag.FirstIdentifier());
                     }
                 }
                 writer.WriteProperty(nullableProp, true);
@@ -753,7 +753,7 @@ private void DowncastTypeArrayToV2OrV3(JsonSchemaType schemaType, IOpenApiWriter
                 }
                 else
                 {
-                    writer.WriteProperty(OpenApiConstants.Type, schemaType.ToIdentifier().FirstOrDefault());
+                    writer.WriteProperty(OpenApiConstants.Type, schemaType.FirstIdentifier());
                 }
             }
         }

src/Microsoft.OpenApi/Validations/Rules/RuleHelpers.cs

@@ -56,7 +56,7 @@ public static void ValidateDataTypeMismatch(
             // convert value to JsonElement and access the ValueKind property to determine the type.
             var valueKind = value.GetValueKind();
 
-            var type = schema.Type.ToIdentifier().FirstOrDefault(x => x is not null);
+            var type = (schema.Type & ~JsonSchemaType.Null)?.FirstIdentifier();
             var format = schema.Format;
 
             // Before checking the type, check first if the schema allows null.