added test for existence of fMagneticField in SetMagField()

diff --git a/AliGeant4/AliModulesComposition.cxx b/AliGeant4/AliModulesComposition.cxx
index d7e92882a6fc39b427dbc9369639ec18f9037e51..ce1a4b7861463fecef2fae1f88a28f2d5f80d3e7 100644 (file)
--- a/AliGeant4/AliModulesComposition.cxx
+++ b/AliGeant4/AliModulesComposition.cxx
@@ -445,7 +445,7 @@ void AliModulesComposition::SetMagField(G4double fieldValue)
 {
 // Sets uniform magnetic field to specified value.
 // ---
-
-  fMagneticField->SetFieldValue(fieldValue);
+  if (fMagneticField)
+    fMagneticField->SetFieldValue(fieldValue);
 }