我在其他帖子中找不到解决方法，
在尝试构建项目时，Eclipse中出现以下错误： （在一个小的弹出窗口中打开）
Errors occurred during the build.
Errors running builder 'Java Builder' on project 'C2S'.
java.lang.NullPointerException
在查看<workspace_dir>\.metadata\.log时，我看到了堆栈跟踪：
!ENTRY org.eclipse.core.resources 4 75 2018-08-06 11:02:18.484
!MESSAGE Errors occurred during the build.
!SUBENTRY 1 org.eclipse.jdt.core 4 75 2018-08-06 11:02:18.484
!MESSAGE Errors running builder 'Java Builder' on project 'C2S'.
!STACK 0
java.lang.NullPointerException
at org.eclipse.jdt.internal.compiler.ast.MessageSend.analyseCode(MessageSend.java:142)
at org.eclipse.jdt.internal.compiler.ast.MessageSend.analyseCode(MessageSend.java:216)
at org.eclipse.jdt.internal.compiler.ast.MethodDeclaration.analyseCode(MethodDeclaration.java:125)
at org.eclipse.jdt.internal.compiler.ast.TypeDeclaration.internalAnalyseCode(TypeDeclaration.java:755)
at org.eclipse.jdt.internal.compiler.ast.TypeDeclaration.analyseCode(TypeDeclaration.java:228)
at org.eclipse.jdt.internal.compiler.ast.TypeDeclaration.internalAnalyseCode(TypeDeclaration.java:716)
at org.eclipse.jdt.internal.compiler.ast.TypeDeclaration.analyseCode(TypeDeclaration.java:263)
at org.eclipse.jdt.internal.compiler.ast.CompilationUnitDeclaration.analyseCode(CompilationUnitDeclaration.java:122)
at org.eclipse.jdt.internal.compiler.Compiler.process(Compiler.java:891)
at org.eclipse.jdt.internal.compiler.ProcessTaskManager.run(ProcessTaskManager.java:141)
at java.lang.Thread.run(Thread.java:748)
Eclipse版本：
Eclipse IDE for Java Developers
Version: Oxygen.3a Release (4.7.3a)