diff --git a/packages/imhotep-dsl/src/compiler.ts b/packages/imhotep-dsl/src/compiler.ts
index 04b741e..bd13669 100644
--- a/packages/imhotep-dsl/src/compiler.ts
+++ b/packages/imhotep-dsl/src/compiler.ts
@@ -73,7 +73,11 @@ function defaultNextId(prefix: string): string {
 
 function normalizeOptionValue(raw: unknown): number | string | undefined {
   if (raw === undefined || raw === null) return undefined
-  if (typeof raw === 'number' || typeof raw === 'string') return raw
+  if (typeof raw === 'number') return Number.isNaN(raw) ? undefined : raw
+  if (typeof raw === 'string') {
+    const trimmed = raw.trim()
+    return trimmed.length > 0 ? trimmed : undefined
+  }
 
   // String-parser/fluent path: LiteralNode or ToleranceLiteralNode
   if (typeof raw === 'object') {
diff --git a/packages/imhotep-dsl/src/grammar.ts b/packages/imhotep-dsl/src/grammar.ts
index 23bd810..25e8afe 100644
--- a/packages/imhotep-dsl/src/grammar.ts
+++ b/packages/imhotep-dsl/src/grammar.ts
@@ -952,6 +952,7 @@ export class GrammarParser {
       if (negated) {
         throw this.error(`Expected assertion after 'not'`)
       }
+      console.warn(`[imhotep-dsl] parseAssertion: unexpected token "${this.currentToken().value}" at line ${this.currentToken().start?.line}, skipping`)
       this.advance()
       return null
     }
@@ -968,6 +969,7 @@ export class GrammarParser {
       if (quantifier) {
         throw this.error(`Expected assertion after quantifier '${quantifier.kind}'`)
       }
+      console.warn(`[imhotep-dsl] parseAssertion: could not parse clause for subject "${subject.value}" at line ${start?.line}, skipping`)
       return null
     }