Retransformation of j.l.i.LambdaForm using j.l.i.Instrumentation::retransformClasses and any registered ClassFileTranformer leads to following assertion:

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/HUDSON/workspace/9-2-build-linux-amd64/jdk9/1503/hotspot/src/share/vm/oops/constantPool.cpp:2050), pid=23388, tid=139660894672640
# assert(sym != NULL) failed: SymbolHashMap::find_entry - symbol is NULL
#
# JRE version: Java(TM) SE Runtime Environment (9.0-b35) (build 1.9.0-ea-fastdebug-b35)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (1.9.0-ea-fastdebug-b35 mixed mode linux-amd64 compressed oops)
# Failed to write core dump. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
#
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
#

Stack: [0x00007f0555f41000,0x00007f0556042000], sp=0x00007f055603f180, free space=1016k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x1087731] VMError::report_and_die()+0x151
V [libjvm.so+0x73d6fb] report_vm_error(char const*, int, char const*, char const*)+0x7b
V [libjvm.so+0x726974] SymbolHashMap::find_entry(Symbol*)+0x114
V [libjvm.so+0x72a40b] ConstantPool::copy_cpool_bytes(int, SymbolHashMap*, unsigned char*)+0x2cb
V [libjvm.so+0xb0dc5c] JvmtiClassFileReconstituter::write_class_file_format()+0x10c
V [libjvm.so+0xb8d33b] JvmtiEnv::RetransformClasses(int, _jclass* const*)+0x4fb
V [libjvm.so+0xb10ee1] jvmti_RetransformClasses+0x141
C [libinstrument.so+0x4543] retransformClasses+0x1f3
j sun.instrument.InstrumentationImpl.retransformClasses0(J[Ljava/lang/Class;)V+0
j sun.instrument.InstrumentationImpl.retransformClasses([Ljava/lang/Class;)V+23
j Agent.premain(Ljava/lang/String;Ljava/lang/instrument/Instrumentation;)V+135
...

With product builds such retransformation cause crash too.

Issue could be reproduced with both 8u and 9 using attached test.