[Analysis API] Avoid exception from getImportAlias.

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/references/FirSimpleNameReference.kt

@@ -65,8 +65,9 @@ internal class KtFirSimpleNameReference(
     }
 
     override fun getImportAlias(): KtImportAlias? {
-        TODO("Not yet implemented")
+        // TODO: Implement.
+        return null
     }
 
     override val resolver get() = KtFirReferenceResolver
-}
+}