add schema exists check

Author: Jan Kaul

datafusion_iceberg/src/catalog/catalog.rs

@@ -43,6 +43,9 @@ impl CatalogProvider for IcebergCatalog {
         }
     }
     fn schema(&self, name: &str) -> Option<Arc<dyn SchemaProvider>> {
+        if !self.catalog.schema_exists(name) {
+            return None;
+        }
         Some(Arc::new(IcebergSchema::new(
             Namespace::try_new(
                 &name

datafusion_iceberg/src/catalog/mirror.rs

@@ -184,6 +184,12 @@ impl Mirror {
         self.storage.contains_key(&identifier.to_string())
     }
 
+    pub fn schema_exists(&self, name: &str) -> bool {
+        self.storage.get(name).map_or(false, |node| {
+            matches!(node.value(), Node::Namespace(_))
+        })
+    }
+
     pub fn catalog(&self) -> Arc<dyn Catalog> {
         self.catalog.clone()
     }