Bugfix: fixed NPE error while getting subtarget of a constraint, not every constraint data have such field

git-svn-id: https://jmonkeyengine.googlecode.com/svn/trunk@9973 75d07b2b-3a1a-0410-a2c5-0572b91ccdca

engine/src/blender/com/jme3/scene/plugins/blender/constraints/Constraint.java

@@ -68,7 +68,10 @@ public abstract class Constraint {
 			if(pTar!= null && pTar.isNotNull()) {
 				this.targetOMA = pTar.getOldMemoryAddress();
 				this.targetSpace = Space.valueOf(((Number) constraintStructure.getFieldValue("tarspace")).byteValue());
-				subtargetName = data.getFieldValue("subtarget").toString();
+				Object subtargetValue = data.getFieldValue("subtarget");
+				if(subtargetValue != null) {//not all constraint data have the subtarget field
+					subtargetName = subtargetValue.toString();
+				}
 			}
 		} else {
 			//Null constraint has no data, so create it here