Fix NullPointerException in SingleTargetMapping when source or suffix…

[NehaSaini011]

Description
This pull request addresses a NullPointerException (NPE) in SingleTargetMapping.java that occurs when evaluating source.endsWith(sourceSuffix) if either source or sourceSuffix is passed as a null value.

To resolve this, a defensive guard clause has been implemented to return an empty set (Collections.emptySet()) immediately if any parameter validation fails, avoiding the crash.

Configuration Details / Changes
Fix Implementation: Added short-circuit null validation for source and sourceSuffix in SingleTargetMapping#getTargetFiles.

Test Isolation & Coverage:

Created a dedicated JUnit 5 test class SingleTargetMappingTest.java to explicitly cover suffix matching, non-matching, and null input edge cases.

Removed the legacy, misplaced test method singleTargetMapper() from SuffixMappingTest.java to clean up duplicate test footprints and enforce correct separation of concerns.

Style & Quality Gates: Fixed all checkstyle rules (avoiding star imports and matching method camelCase patterns) to ensure compliance with project conventions.

Closes #94

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[Copilot]

Pull request overview

This PR fixes a NullPointerException in SingleTargetMapping#getTargetFiles by short-circuiting when source or sourceSuffix is null, and reorganizes test coverage by moving SingleTargetMapping expectations into a dedicated test class.

Changes:

• Add a null-guard in SingleTargetMapping#getTargetFiles before calling source.endsWith(sourceSuffix).
• Add SingleTargetMappingTest to cover suffix match/non-match and null-input behavior.
• Remove the previously misplaced SingleTargetMapping test from SuffixMappingTest.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/main/java/org/apache/maven/shared/io/scan/mapping/SingleTargetMapping.java	Adds a defensive null check to prevent NPE during suffix evaluation.
src/test/java/org/apache/maven/shared/io/scan/mapping/SingleTargetMappingTest.java	Introduces dedicated tests for SingleTargetMapping behavior and null handling.
src/test/java/org/apache/maven/shared/io/scan/mapping/SuffixMappingTest.java	Removes the unrelated SingleTargetMapping test to keep responsibilities separated.

Suppressed comments (1)

src/test/java/org/apache/maven/shared/io/scan/mapping/SingleTargetMappingTest.java:60

• The null-handling test currently calls getTargetFiles(..., null) with a null source, but it doesn't cover the reported NPE case where source is non-null and sourceSuffix is null (i.e. source.endsWith(null)). Adding an assertion for the non-null source + null suffix path ensures the regression is actually covered.

    void testGetTargetFilesShouldHandleNullSourceAndSuffixGracefully() {
        SingleTargetMapping mapping = new SingleTargetMapping(null, "/foo");
        File basedir = new File("target/");

        assertDoesNotThrow(() -> {
            Set<File> results = mapping.getTargetFiles(basedir, null);
            assertTrue(results.isEmpty());

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