diff --git a/packages/das/src/api/miners/miners.service.ts b/packages/das/src/api/miners/miners.service.ts
index 180953f..801d01b 100644
--- a/packages/das/src/api/miners/miners.service.ts
+++ b/packages/das/src/api/miners/miners.service.ts
@@ -202,6 +202,7 @@ export class MinersService {
             AND sp.pr_number      = i.solved_by_pr
             -- Skip null-author solving PRs (no one to credit)
             AND sp.author_github_id IS NOT NULL
+            AND BTRIM(sp.author_github_id) <> ''
             -- Skip corrupted MERGED-without-merged_at shape
             AND NOT (sp.state = 'MERGED' AND sp.merged_at IS NULL)
         ) AS solving_pr
diff --git a/packages/das/src/webhook/github-fetcher.service.ts b/packages/das/src/webhook/github-fetcher.service.ts
index 88ad900..2ea4cda 100644
--- a/packages/das/src/webhook/github-fetcher.service.ts
+++ b/packages/das/src/webhook/github-fetcher.service.ts
@@ -784,7 +784,10 @@ export class GitHubFetcherService implements OnModuleInit {
           {
             repoFullName,
             prNumber: pr.number,
-            authorGithubId: String(pr.author?.databaseId ?? ""),
+            authorGithubId:
+              pr.author?.databaseId != null
+                ? String(pr.author.databaseId)
+                : null,
             authorLogin: pr.author?.login ?? null,
             authorAssociation: pr.authorAssociation ?? null,
             title: pr.title,
diff --git a/packages/db/26_normalize_blank_pr_author_ids.sql b/packages/db/26_normalize_blank_pr_author_ids.sql
new file mode 100644
index 0000000..3be1cd0
--- /dev/null
+++ b/packages/db/26_normalize_blank_pr_author_ids.sql
@@ -0,0 +1,7 @@
+-- Normalize legacy bad rows where unknown PR author IDs were stored as blanks.
+-- Unknown author identity must be NULL so solver-credit filters can exclude it.
+
+UPDATE pull_requests
+SET author_github_id = NULL
+WHERE author_github_id IS NOT NULL
+  AND BTRIM(author_github_id) = '';