Add input validation guidelines and enhance cleanParams function to preserve default values

client/src/utils/paramUtils.ts

@@ -2,7 +2,7 @@ import type { JsonSchemaType } from "./jsonUtils";
 
 /**
  * Cleans parameters by removing undefined, null, and empty string values for optional fields
- * while preserving all values for required fields.
+ * while preserving all values for required fields and fields with explicit default values.
  *
  * @param params - The parameters object to clean
  * @param schema - The JSON schema defining which fields are required
@@ -14,13 +14,23 @@ export function cleanParams(
 ): Record<string, unknown> {
   const cleaned: Record<string, unknown> = {};
   const required = schema.required || [];
+  const properties = schema.properties || {};
 
   for (const [key, value] of Object.entries(params)) {
     const isFieldRequired = required.includes(key);
+    const fieldSchema = properties[key] as JsonSchemaType | undefined;
+
+    // Check if the field has an explicit default value
+    const hasDefault = fieldSchema && "default" in fieldSchema;
+    const defaultValue = hasDefault ? fieldSchema.default : undefined;
 
     if (isFieldRequired) {
       // Required fields: always include, even if empty string or falsy
       cleaned[key] = value;
+    } else if (hasDefault && value === defaultValue) {
+      // Field has a default value and current value matches it - preserve it
+      // This is important for cases like default: null
+      cleaned[key] = value;
     } else {
       // Optional fields: only include if they have meaningful values
       if (value !== undefined && value !== "" && value !== null) {