check_nullable does not uselessly compute isna() anymore in pandas backend. Fixed #1533

Author: Sylvain MARIE

pandera/backends/pandas/array.py

@@ -194,8 +194,16 @@ def check_name(self, check_obj: pd.Series, schema) -> CoreCheckResult:
 
     @validate_scope(scope=ValidationScope.SCHEMA)
     def check_nullable(self, check_obj: pd.Series, schema) -> CoreCheckResult:
+        if schema.nullable:
+            # Avoid to compute anything for perf reasons. GH#1533
+            return CoreCheckResult(
+                passed=True,
+                check="not_nullable",
+            )
+
+        # Check actual column contents
         isna = check_obj.isna()
-        passed = schema.nullable or not isna.any()
+        passed = not isna.any()
         return CoreCheckResult(
             passed=cast(bool, passed),
             check="not_nullable",