Fix Security Analysis exception contingency on half-connected non-impedance branch

[jeandemanged]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• A PR or issue has been opened in all impacted repositories (if any)

Does this PR already have an issue describing the problem?

No

What kind of change does this PR introduce?

Bug fix

What is the current behavior?

With lowImpedanceBranchMode set to REPLACE_BY_ZERO_IMPEDANCE_LINE, contingencies on non-impedant branches that are connected only at one side cause an exception, in both AC and DC.

Caused by: java.util.NoSuchElementException: No value present
	at java.base/java.util.Optional.orElseThrow(Optional.java:377)
	at com.powsybl.openloadflow.ac.equations.AcEquationSystemUpdater.updateNonImpedantBranchEquations(AcEquationSystemUpdater.java:77)
	at com.powsybl.openloadflow.lf.AbstractEquationSystemUpdater.updateElementEquations(AbstractEquationSystemUpdater.java:49)
	at com.powsybl.openloadflow.ac.equations.AcEquationSystemUpdater.onDisableChange(AcEquationSystemUpdater.java:93)
	at com.powsybl.openloadflow.network.LfNetworkListenerTracer.onDisableChange(LfNetworkListenerTracer.java:118)
	at com.powsybl.openloadflow.network.AbstractElement.notifyDisable(AbstractElement.java:61)
	at com.powsybl.openloadflow.network.impl.AbstractLfBranch.setDisabled(AbstractLfBranch.java:439)
	at com.powsybl.openloadflow.network.LfContingency.apply(LfContingency.java:134)

What is the new behavior (if this is a feature change)?

The fix consists in adding a check that both buses of the branch are non-null when updating non-impedant branches equations. (Because non-impedant branches equations are created only if both buses of the branch are non-null).

Does this PR introduce a breaking change or deprecate an API?

• No

Other information:

The issue was first observed on a three-windings transformer with one side disconnected (if this matters), but can be reproduced on a simple line.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud