refactor: change schema fields from optional to nullable

lib/types.ts

@@ -34,16 +34,31 @@ export const configSchema = z
     title: z.string(),
     xKey: z.string().describe("Key for x-axis or category"),
     yKeys: z.array(z.string()).describe("Key(s) for y-axis values this is typically the quantitative column"),
-    multipleLines: z.boolean().describe("For line charts only: whether the chart is comparing groups of data.").optional(),
-    measurementColumn: z.string().describe("For line charts only: key for quantitative y-axis column to measure against (eg. values, counts etc.)").optional(),
-    lineCategories: z.array(z.string()).describe("For line charts only: Categories used to compare different lines or data series. Each category represents a distinct line in the chart.").optional(),
+    multipleLines: z
+      .boolean()
+      .nullable()
+      .describe(
+        "For line charts only: whether the chart is comparing groups of data.",
+      ),
+    measurementColumn: z
+      .string()
+      .nullable()
+      .describe(
+        "For line charts only: key for quantitative y-axis column to measure against (eg. values, counts etc.)",
+      ),
+    lineCategories: z
+      .array(z.string())
+      .nullable()
+      .describe(
+        "For line charts only: Categories used to compare different lines or data series. Each category represents a distinct line in the chart.",
+      ),
     colors: z
       .record(
         z.string().describe("Any of the yKeys"),
         z.string().describe("Color value in CSS format (e.g., hex, rgb, hsl)"),
       )
-      .describe("Mapping of data keys to color values for chart elements")
-      .optional(),
+      .nullable()
+      .describe("Mapping of data keys to color values for chart elements"),
     legend: z.boolean().describe("Whether to show legend"),
   })
   .describe("Chart configuration object");