fix: raise ValidationError for empty OpenQASM loads()

CHANGELOG.md

@@ -23,6 +23,7 @@ Types of changes:
 ### Removed
 
 ### Fixed
+- Fixed `loads("")` / whitespace-only input raising `AttributeError` instead of `ValidationError`. Empty and whitespace programs now raise `ValidationError` like other parse failures. ([#451](https://github.com/qBraid/pyqasm/pull/451), [#437](https://github.com/qBraid/pyqasm/issues/437))
 
 ### Dependencies
 

src/pyqasm/entrypoint.py

@@ -182,7 +182,8 @@ def loads(program: openqasm3.ast.Program | str, **kwargs) -> QasmModule:
         program, opaque_gates = rewrite_opaque_declarations(program)
         try:
             program = openqasm3.parse(program)
-        except openqasm3.parser.QASM3ParsingError as err:
+        except (openqasm3.parser.QASM3ParsingError, AttributeError) as err:
+            # openqasm3 can raise AttributeError on empty/whitespace-only input
             raise ValidationError(f"Failed to parse OpenQASM string: {err}") from err
     elif not isinstance(program, openqasm3.ast.Program):
         raise TypeError("Input quantum program must be of type 'str' or 'openqasm3.ast.Program'.")

tests/qasm3/test_entrypoint.py

@@ -74,3 +74,17 @@ def test_incorrect_module_unroll_raises_error():
     with pytest.raises(ValidationError):
         module = loads("OPENQASM 3.0;\n qubit q; h q[2]")
         module.unroll()
+
+
+def test_loads_empty_string_raises_validation_error():
+    """Empty / whitespace-only input must raise ValidationError, not AttributeError."""
+    for program in ("", "   ", "\n\t"):
+        with pytest.raises(ValidationError, match="Failed to parse OpenQASM string"):
+            loads(program)
+
+
+def test_loads_header_only_module_ok():
+    """A header-only OpenQASM 3 program (no statements) remains valid."""
+    module = loads("OPENQASM 3.0;\n")
+    assert module.num_qubits == 0
+    assert module.num_clbits == 0