[Bug]: NullPointerException with `getsignal`

Describe the bug

GraalPy crashes when running this fuzzed code:

from signal import getsignal
getsignal(0)

Operating system

Linux

CPU architecture

x86_64

GraalPy version

GraalPy 3.13.14 (Oracle GraalVM Native 25.3.4.1)

JDK version

No response

Context configuration

No response

Steps to reproduce

Snippet listed above

Expected behavior

No crash

Stack trace

java.lang.NullPointerException: name
	at java.base@25.0.4.1/java.util.Objects.requireNonNull(Objects.java:246)
	at java.base@25.0.4.1/jdk.internal.misc.Signal.<init>(Signal.java:138)
	at jdk.unsupported@25.0.4.1/sun.misc.Signal.<init>(Signal.java:139)
	at org.graalvm.py/com.oracle.graal.python.builtins.modules.Signals.getCurrentSignalHandler(SignalModuleBuiltins.java:651)
	at org.graalvm.py/com.oracle.graal.python.builtins.modules.SignalModuleBuiltins$GetSignalNode.getsignal(SignalModuleBuiltins.java:341)
	at org.graalvm.py/com.oracle.graal.python.builtins.modules.SignalModuleBuiltinsFactory$GetSignalNodeFactory$GetSignalNodeGen.executeWithoutClinic(SignalModuleBuiltinsFactory.java:312)
	at org.graalvm.py/com.oracle.graal.python.nodes.function.builtins.PythonBinaryClinicBuiltinNode.execute(PythonBinaryClinicBuiltinNode.java:84)
	at org.graalvm.py/com.oracle.graal.python.nodes.function.builtins.BuiltinCallNode$BuiltinBinaryCallNode.execute(BuiltinCallNode.java:106)
	at org.graalvm.py/com.oracle.graal.python.nodes.function.BuiltinFunctionRootNode.execute(BuiltinFunctionRootNode.java:337)
	at org.graalvm.truffle.runtime/com.oracle.truffle.runtime.OptimizedCallTarget.executeRootNode(OptimizedCallTarget.java:808)
	at org.graalvm.truffle.runtime/com.oracle.truffle.runtime.OptimizedCallTarget.profiledPERoot(OptimizedCallTarget.java:722)
	at org.graalvm.truffle.runtime/com.oracle.truffle.runtime.OptimizedCallTarget.callBoundary(OptimizedCallTarget.java:641)
	at org.graalvm.truffle.runtime.svm/com.oracle.svm.truffle.api.SubstrateOptimizedCallTarget.invokeCallBoundary(SubstrateOptimizedCallTarget.java:124)
	at com.oracle.truffle.enterprise.svm/com.oracle.svm.enterprise.truffle.compiler.SubstrateEnterpriseOptimizedCallTarget.invokeCompiledAdapterOrCallBoundary(SubstrateEnterpriseOptimizedCallTarget.java:293)
	at com.oracle.truffle.enterprise.svm/com.oracle.svm.enterprise.truffle.compiler.SubstrateEnterpriseOptimizedCallTarget.invokeFromInterpreter(SubstrateEnterpriseOptimizedCallTarget.java:269)
	at com.oracle.truffle.enterprise.svm/com.oracle.svm.enterprise.truffle.compiler.SubstrateEnterpriseOptimizedCallTarget.doInvoke(SubstrateEnterpriseOptimizedCallTarget.java:255)
	at org.graalvm.truffle.runtime/com.oracle.truffle.runtime.OptimizedCallTarget.callDirect(OptimizedCallTarget.java:573)
	at org.graalvm.truffle.runtime/com.oracle.truffle.runtime.OptimizedCallTarget.call(OptimizedCallTarget.java:519)
	at org.graalvm.truffle/com.oracle.truffle.api.nodes.IndirectCallNode$1.call(IndirectCallNode.java:96)
	at org.graalvm.py/com.oracle.graal.python.nodes.call.CallDispatchers$SimpleIndirectInvokeNode.doIndirect(CallDispatchers.java:167)
	at org.graalvm.py/com.oracle.graal.python.nodes.call.CallDispatchersFactory$SimpleIndirectInvokeNodeGen$Uncached.execute(CallDispatchersFactory.java:307)
	at org.graalvm.py/com.oracle.graal.python.nodes.call.CallDispatchers$BuiltinMethodCachedCallNode.callBuiltinMethodMegamorphic(CallDispatchers.java:324)
	at org.graalvm.py/com.oracle.graal.python.nodes.call.CallDispatchersFactory$BuiltinMethodCachedCallNodeGen$Uncached.execute(CallDispatchersFactory.java:1758)
	at org.graalvm.py/com.oracle.graal.python.nodes.call.CallNode.builtinMethodCall(CallNode.java:187)
	at org.graalvm.py/com.oracle.graal.python.nodes.call.CallNodeGen$Uncached.executeInternal(CallNodeGen.java:627)
	at org.graalvm.py/com.oracle.graal.python.nodes.call.CallNode.execute(CallNode.java:128)
	at org.graalvm.py/com.oracle.graal.python.nodes.call.special.CallBinaryMethodNode.call(CallBinaryMethodNode.java:181)
	at org.graalvm.py/com.oracle.graal.python.nodes.bytecode_dsl.PBytecodeDSLRootNodeGen$CallBinaryMethod_Node.execute$uncached(PBytecodeDSLRootNodeGen.java)
	at org.graalvm.py/com.oracle.graal.python.nodes.bytecode_dsl.PBytecodeDSLRootNodeGen$UncachedBytecodeNodeTailCall.handleCallBinaryMethod_(PBytecodeDSLRootNodeGen.java:37865)
	at org.graalvm.py/com.oracle.graal.python.nodes.bytecode_dsl.PBytecodeDSLRootNodeGen$UncachedBytecodeNodeTailCall.__stub_handleCallBinaryMethod_(PBytecodeDSLRootNodeGen.java:0)
	at org.graalvm.py/com.oracle.graal.python.nodes.bytecode_dsl.PBytecodeDSLRootNodeGen$UncachedBytecodeNodeTailCall.continueAt(PBytecodeDSLRootNodeGen.java:35093)
	at org.graalvm.py/com.oracle.graal.python.nodes.bytecode_dsl.PBytecodeDSLRootNodeGen.continueAt(PBytecodeDSLRootNodeGen.java:3501)
	at org.graalvm.py/com.oracle.graal.python.nodes.bytecode_dsl.PBytecodeDSLRootNodeGen.execute(PBytecodeDSLRootNodeGen.java:3493)
[...snip...]

Additional context

No response

Start by reproducing the Python snippet from signal import getsignal; getsignal(0) on Linux, then inspect SignalModuleBuiltins.java, especially Signals.getCurrentSignalHandler and GetSignalNode.getsignal from the stack trace. Done means the call no longer raises a Java NullPointerException; add or run the relevant signal regression coverage if the project provides it.