FULL PRODUCT VERSION :
java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.51-b03, mixed mode)

javac 1.8.0_51

FULL OS VERSION :
Darwin Kernel Version 14.4.0: Thu May 28 11:35:04 PDT 2015; root:xnu-2782.30.5~1/RELEASE_X86_64 x86_64

A DESCRIPTION OF THE PROBLEM :
Compiling code that resembles the code in 'Testing.java' file here with the above Java compiler version:

https://github.com/leothekim/javac-1.8.0_51-b16-NPE

Results in the following error:

java.lang.NullPointerException
        at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.visitIdent(Flow.java:2377)
        at com.sun.tools.javac.tree.JCTree$JCIdent.accept(JCTree.java:2011)
        at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
        at com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:404)
        ..


THE PROBLEM WAS REPRODUCIBLE WITH -Xint FLAG: Did not try

THE PROBLEM WAS REPRODUCIBLE WITH -server FLAG: Did not try

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the Testing.java file in the github repo above.

EXPECTED VERSUS ACTUAL BEHAVIOR :
I would have expected a friendly compiler message saying that "Strings::new" is an invalid symbol, or something along those lines. The NPE is an incorrect failure mode for the compiler.
ERROR MESSAGES/STACK TRACES THAT OCCUR :
An exception has occurred in the compiler (1.8.0_51). Please file a bug at the Java Developer Connection (http://java.sun.com/webapps/bugreport) after checking the Bug Parade for duplicates. Include your program and the following diagnostic in your report. Thank you.
java.lang.NullPointerException
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.visitIdent(Flow.java:2377)
at com.sun.tools.javac.tree.JCTree$JCIdent.accept(JCTree.java:2011)
at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
at com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:404)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.scan(Flow.java:1382)
at com.sun.tools.javac.tree.TreeScanner.visitReference(TreeScanner.java:268)
at com.sun.tools.javac.tree.JCTree$JCMemberReference.accept(JCTree.java:1973)
at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
at com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:404)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.scan(Flow.java:1382)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.scanExpr(Flow.java:1624)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.scanExprs(Flow.java:1636)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.visitApply(Flow.java:2233)
at com.sun.tools.javac.tree.JCTree$JCMethodInvocation.accept(JCTree.java:1465)
at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
at com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:404)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.scan(Flow.java:1382)
at com.sun.tools.javac.tree.TreeScanner.visitExec(TreeScanner.java:175)
at com.sun.tools.javac.tree.JCTree$JCExpressionStatement.accept(JCTree.java:1296)
at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
at com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:404)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.scan(Flow.java:1382)
at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:57)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.visitBlock(Flow.java:1843)
at com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:909)
at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
at com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:404)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.scan(Flow.java:1382)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.visitMethodDef(Flow.java:1780)
at com.sun.tools.javac.comp.Flow$AssignAnalyzer.visitMethodDef(Flow.java:2546)
at com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:778)
at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
at com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:404)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.scan(Flow.java:1382)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.visitClassDef(Flow.java:1733)
at com.sun.tools.javac.comp.Flow$AssignAnalyzer.visitClassDef(Flow.java:2525)
at com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:693)
at com.sun.tools.javac.tree.TreeScanner.scan(TreeScanner.java:49)
at com.sun.tools.javac.comp.Flow$BaseAnalyzer.scan(Flow.java:404)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.scan(Flow.java:1382)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.analyzeTree(Flow.java:2420)
at com.sun.tools.javac.comp.Flow$AbstractAssignAnalyzer.analyzeTree(Flow.java:2403)
at com.sun.tools.javac.comp.Flow.analyzeTree(Flow.java:211)
at com.sun.tools.javac.main.JavaCompiler.flow(JavaCompiler.java:1327)
at com.sun.tools.javac.main.JavaCompiler.flow(JavaCompiler.java:1296)
at com.sun.tools.javac.main.JavaCompiler.compile2(JavaCompiler.java:901)
at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:860)
at com.sun.tools.javac.main.Main.compile(Main.java:523)
at com.sun.tools.javac.main.Main.compile(Main.java:381)
at com.sun.tools.javac.main.Main.compile(Main.java:370)
at com.sun.tools.javac.main.Main.compile(Main.java:361)
at com.sun.tools.javac.Main.compile(Main.java:56)
at com.sun.tools.javac.Main.main(Main.java:42)

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
Source code found here:
https://github.com/leothekim/javac-1.8.0_51-b16-NPE

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
The solution is to provide a valid method reference, e.g. "String::new" instead of "Strings::new".