#vulnerable code 
                             public static double heightDegrees(int n) {
		if (hashHeightCache.get(n) == null) {
			double a;
			if (n % 2 == 0)
				a = -1;
			else
				a = -0.5;
			double result = 90 / Math.pow(2, 2.5 * n + a);
			hashHeightCache.put(n, result);
		}
		return hashHeightCache.get(n);
	} 
                            #location 11 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             public static double heightDegrees(int n) {
		if (hashHeightCache[n - 1] == null) {
			double a;
			if (n % 2 == 0)
				a = -1;
			else
				a = -0.5;
			double result = 90 / Math.pow(2, 2.5 * n + a);
			hashHeightCache[n - 1] = result;
		}
		return hashHeightCache[n - 1];
	}