I want to open a new strategy inside another strategy based upon the outcome of that strategy.
So I wrote inside an If statement :

File file = new File("C:/Users/Documents/JForex/Strategies/Files/Strategy1.jfx");
IStrategyListener listener = new IStrategyListener() {public void onStart(long strategyId){} public void onStop(long strategyId){}};
Map paraMap = new HashMap();
paraMap.put("Instrument", selectedInstrument);
strategy.startStrategy(file, listener, paraMap, true);

The strategy compiled without errors, but when the method startStrategy is called it throws a nullpointerexception.
I think this has something to do with the file.

I could just copy past the whole strategy into the other so it becomes 1 very large one. Does anybody know what I could do?

To execute a strategy logic of another strategy consider from JForex plaform, consider the following approach:
https://www.dukascopy.com/wiki/#Multiple_strategies_within_a_strategy
To run multiple strategies from JForex SDK, consider the following approach:
https://www.dukascopy.com/wiki/#JForex_SDK/Running_strategies