Can SPF support test case generation for string input?

[Minjuner-97]

Hello~
In order to generate test case ,in progress jpf-symbc, I run the jpf : strings.HelloWorld.jpf.
In results, I can't get the test case ,but only search start.
So, can SPF support test case generation for string input?
the output as follows:

[WARNING] unknown classpath element: /home/zhou/PROJECTS/tmp/jpf2/jpf-core/build/jpf-classes.jar
Running Symbolic PathFinder ...
symbolic.dp=choco
symbolic.string_dp_timeout_ms=3000
symbolic.string_dp=abc
symbolic.choco_time_bound=30000
symbolic.max_pc_length=2147483647
symbolic.max_pc_msec=0
symbolic.bvlength=32
symbolic.min_int=-2147483648
symbolic.min_long=-9223372036854775808
symbolic.min_short=-32768
symbolic.min_byte=-128
symbolic.min_char=0
symbolic.max_int=2147483647
symbolic.max_long=9223372036854775807
symbolic.max_short=32767
symbolic.max_byte=127
symbolic.max_char=65535
symbolic.min_double=4.9E-324
symbolic.max_double=1.7976931348623157E308
JavaPathfinder core system v8.0 - (C) 2005-2014 United States Government. All rights reserved.

====================================================== system under test
strings.HelloWorld.main()

====================================================== search started: 8/10/22 5:25 AM
null
New sym int var_1_1_SYMSTRING.length min=-2147483648, max=2147483647

Warning: empty path condition

PCs: total:1 sat:1 unsat:0

string analysis: SPC # = 1
(var_1_1_SYMSTRING notequals CONST_Hello, World!)
NPC constraint # = 0
string analysis: SPC # = 1
(var_1_1_SYMSTRING notequals CONST_Hello, World!)
NPC constraint # = 0
Summary**
PC is:constraint # = 0

Warning: empty path condition

PCs: total:2 sat:2 unsat:0

string analysis: SPC # = 1
(var_1_1_SYMSTRING equals CONST_Hello, World!)
NPC constraint # = 0
Symbolic Exp [ var_1_1_SYMSTRING]
string analysis: SPC # = 1
(var_1_1_SYMSTRING equals CONST_Hello, World!)
NPC constraint # = 0
Summary**
PC is:constraint # = 0

====================================================== Method Summaries
Inputs: var_1_1_SYMSTRING
No path conditions for strings.HelloWorld.hello(java.lang.String@15d)

====================================================== Method Summaries (HTML)

Test Cases Generated by Symbolic JavaPath Finder for strings.HelloWorld.hello (Path Coverage)

No path conditions for strings.HelloWorld.hello(java.lang.String@15d)

====================================================== results
no errors detected

====================================================== statistics
elapsed time: 00:00:00
states: new=3,visited=0,backtracked=3,end=2
search: maxDepth=2,constraints=0
choice generators: thread=1 (signal=0,lock=1,sharedRef=0,threadApi=0,reschedule=0), data=1
heap: new=354,released=22,maxLive=350,gcCycles=3
instructions: 3155
max memory: 234MB
loaded code: classes=60,methods=1295

====================================================== search finished: 8/10/22 5:25 AM

Looking forward to your reply!