probe exisitence of path

    vars:
      a: aaa
      b: bbb
      sydney_grammar:
        address: sydney
    tasks:
    - name: task
      task:
      - func: cmd
        desc: |
          access a non-exist var will not cause error or panic while you render it
        do:
        - name: print
          cmd: '{{.c}}'
      - func: cmd
        desc: |
          however if you access a non exist child element, then it will result in a warning error
        do:
        - name: print
          cmd: '{{.b.not_exist}}'
      - func: cmd
        do:
        - name: query
          desc: |
            if the sub element does not exist, eg school_name does not exit, then the query result will give the result of the closest element result, in this caes the parent value "aaa" will be return
          cmd:
            path: a.school_name
            reg: myschool
        - name: query
          cmd:
            path: sydney_grammar.address
            reg: school_address
        - name: pathExisted
          cmd:
            path: sydney_grammar.address
            reg: address_existed
        - name: pathExisted
          desc: |
            the state will be rendered as <no value>, this will be treated as not exist
          cmd:
            path: sydney_grammar.state
            reg: state_existed
        - name: pathExisted
          cmd:
            path: b.not_exist
            reg: varb_sub_element_existed
        - name: print
          cmd: |
            sydney_grammar.address exist: {{.address_existed}}
            sydney_grammar.state exist: {{.state_existed}}
            varb_sub_element_existed exist: {{.varb_sub_element_existed}}
      - func: cmd
        desc: test pathExisted in templating
        do:
        - name: print
          cmd: |
            sydney_grammar.address exist: {{ pathExisted "sydney_grammar.address" }}
            sydney_grammar.state exist: {{ pathExisted "sydney_grammar.state"}}
            varb_sub_element_existed exist: {{ pathExisted "b.not_exist"}}
            {{ if pathExisted "b.not_exist"}}
            I am happy
            {{ else }}
            I am sad
            {{ end }}
      - func: cmd
        do:
        - name: inspect
          cmd:
          - exec_vars
        - name: assert
          cmd:
          - '{{pathExisted "sydney_grammar.address" }}'
    

    loading [Config]:  ./tests/functests/upconfig.yml
    Main config:
                 Version -> 1.0.0
                  RefDir -> ./tests/functests
                 WorkDir -> cwd
              AbsWorkDir -> /up_project/up
                TaskFile -> c0154
                 Verbose -> vvv
              ModuleName -> self
               ShellType -> /bin/sh
           MaxCallLayers -> 8
                 Timeout -> 3600000
     MaxModuelCallLayers -> 256
               EntryTask -> task
      ModRepoUsernameRef -> 
      ModRepoPasswordRef -> 
    work dir: /up_project/up
    -exec task: task
    loading [Task]:  ./tests/functests/c0154
    module: [self], instance id: [dev], exec profile: []
    profile -  envVars:
    
    (*core.Cache)({
    })
    
    Task1: [task ==> task:  ]
    -Step1: [
    access a non-exist var will not cause error or panic while you render it
    ]
    self: final context exec vars:
    
    (*core.Cache)({
      "a": "aaa",
      "b": "bbb",
      "up_runtime_task_layer_number": 0,
      "sydney_grammar": {
        "address": "sydney"
      }
    })
    
    ~SubStep1: [print:  ]
    None
    -Step2: [
    however if you access a non exist child element, then it will result in a warning error
    ]
    self: final context exec vars:
    
    (*core.Cache)({
      "sydney_grammar": {
        "address": "sydney"
      },
      "a": "aaa",
      "b": "bbb",
      "up_runtime_task_layer_number": 0
    })
    
    ~SubStep1: [print:  ]
          template rendering -> template: .:1:4: executing "." at <.b.not_exist>: can't evaluate field not_exist in type interface {}
    WARN:
        1:{{.b.not_exist}}
    
    trouble shooting tips:
    <incompatible types for comparison>: the variable might not be registered, use -v vvv to see the cache, or use inspect cmd to debug
    
    
    -Step3:
    self: final context exec vars:
    
    (*core.Cache)({
      "sydney_grammar": {
        "address": "sydney"
      },
      "a": "aaa",
      "b": "bbb",
      "up_runtime_task_layer_number": 0
    })
    
    ~SubStep1: [query: if the sub element does not exist, eg school_name does not exit, then the query result will give the result of the closest element result, in this caes the parent value "aaa" will be return
     ]
    ~SubStep2: [query:  ]
    ~SubStep3: [pathExisted:  ]
    ~SubStep4: [pathExisted: the state will be rendered as <no value>, this will be treated as not exist
     ]
    ~SubStep5: [pathExisted:  ]
          element validating problem -> template: validator:1:4: executing "validator" at <.b.not_exist>: can't evaluate field not_exist in type interface {}
    WARN:
        1:{{.b.not_exist}}
    
    ~SubStep6: [print:  ]
    sydney_grammar.address exist: true
    sydney_grammar.state exist: false
    varb_sub_element_existed exist: false
    
    -Step4: [: test pathExisted in templating ]
    self: final context exec vars:
    
    (*core.Cache)({
      "sydney_grammar": {
        "address": "sydney"
      },
      "b": "bbb",
      "a": "aaa",
      "myschool": (*string)("aaa"),
      "school_address": (*string)("sydney"),
      "state_existed": false,
      "varb_sub_element_existed": false,
      "address_existed": true,
      "up_runtime_task_layer_number": 0
    })
    
    ~SubStep1: [print:  ]
          element validating problem -> template: validator:1:4: executing "validator" at <.b.not_exist>: can't evaluate field not_exist in type interface {}
    WARN:
        1:{{.b.not_exist}}
    
          element validating problem -> template: validator:1:4: executing "validator" at <.b.not_exist>: can't evaluate field not_exist in type interface {}
    WARN:
        1:{{.b.not_exist}}
    
    sydney_grammar.address exist: true
    sydney_grammar.state exist: false
    varb_sub_element_existed exist: false
    
    I am sad
    
    
    -Step5:
    self: final context exec vars:
    
    (*core.Cache)({
      "b": "bbb",
      "up_runtime_task_layer_number": 0,
      "state_existed": false,
      "myschool": (*string)("aaa"),
      "varb_sub_element_existed": false,
      "sydney_grammar": {
        "address": "sydney"
      },
      "a": "aaa",
      "school_address": (*string)("sydney"),
      "address_existed": true
    })
    
    ~SubStep1: [inspect:  ]
     1: inspect[exec_vars]
    (*core.Cache)({
      "myschool": (*string)("aaa"),
      "state_existed": false,
      "varb_sub_element_existed": false,
      "sydney_grammar": {
        "address": "sydney"
      },
      "a": "aaa",
      "b": "bbb",
      "up_runtime_task_layer_number": 0,
      "school_address": (*string)("sydney"),
      "address_existed": true
    })
    
    ~SubStep2: [assert:  ]
     1 ASSERT OK:     [{{pathExisted "sydney_grammar.address" }}]