fix: preserve result optionality in override

Author: avallete

src/PostgrestBuilder.ts

@@ -219,7 +219,7 @@ export default abstract class PostgrestBuilder<Result, ThrowOnError extends bool
    * Override the type of the returned `data`.
    *
    * @typeParam NewResult - The new result type to override with
-   * @deprecated Use overrideTypes<yourType, { partial: false }>() method at the end of your call chain instead
+   * @deprecated Use overrideTypes<yourType, { merge: false }>() method at the end of your call chain instead
    */
   returns<NewResult>(): PostgrestBuilder<CheckMatchingArrayTypes<Result, NewResult>, ThrowOnError> {
     return this as unknown as PostgrestBuilder<

src/types.ts

@@ -1,4 +1,5 @@
 import PostgrestError from './PostgrestError'
+import { ContainsNull } from './select-query-parser/types'
 import { SelectQueryError } from './select-query-parser/utils'
 
 export type Fetch = typeof fetch
@@ -110,4 +111,8 @@ export type CheckMatchingArrayTypes<Result, NewResult> =
     ? {
         Error: 'Type mismatch: Cannot cast single object to array type. Remove Array wrapper from return type or make sure you are not using .single() up in the calling chain'
       }
-    : NewResult // Neither are arrays - valid
+    : // Neither are arrays - valid
+    // Preserve the optionality of the result if the overriden type is an object (case of chaining with `maybeSingle`)
+    ContainsNull<Result> extends true
+    ? NewResult | null
+    : NewResult

test/returns.test-d.ts

@@ -31,7 +31,7 @@ const postgrest = new PostgrestClient<Database>(REST_URL)
     throw new Error(maybeSingleResult.error.message)
   }
   let maybeSingleResultType: typeof maybeSingleResult.data
-  let maybeSingleExpected: { username: string }
+  let maybeSingleExpected: { username: string } | null
   expectType<TypeEqual<typeof maybeSingleResultType, typeof maybeSingleExpected>>(true)
 
   // Test array to non-array type casting error