solve method always returns null when no solverOptions are provided

[MatthiasVanMeerbeek]

java-spring-decisionrules version: 2.0.4

The response from DecisionRulesService.solve() is always null when it is called without providing solverOptions. Or more specific, when SolveApi.solveAPI() is called with solverOptions set to null.

This issue wasn't present in version 2.0.3 and looks like it was introduced with recent code changes in version 2.0.4.

Previously, the createHeaders method, that is called inside the SolveApi.solveAPI method, used the SolverOptions constructor, but this was changed to a builder (without providing values like was done with the constructor).

createHeaders(
                            options.solverKey,
                            solverOptions != null ? solverOptions
                                    : new SolverOptions(
                                            false,
                                            null,
                                            false,
                                            null)));

createHeaders(
                            options.solverKey,
                            solverOptions != null ? solverOptions
                                    : new SolverOptions.Builder().build()));

The createHeaders method implementation was also changed. All values are null-checked, except "debug" which causes a NullPointerException on:

headers.set("X-Debug", solverOptions.getDebug().toString());

[MatthiasVanMeerbeek]

It looks like I'm not able to create a branch and/or create a pull request.
This should fix it:

headers.set("X-Debug", solverOptions.getDebug() != null ? solverOptions.getDebug().toString() : "false");