Document upload field

Interface Definition: Expression evaluation error [evaluation ID = af95d:a8823] : An error occurred while executing a save: Expression evaluation error: The save target must be a local variable that does not refresh on every evaluation or on an interval, a process variable, or a node input (or a rule input passed one of those three), but instead was: [documentId=, mappingKey=1, entityType=, entityId=, docType=, docName=, docExtension=, docDescription=, appianDocId=, isActive=, createdBy=, createdDate=, lastUpdatedBy=, lastUpdatedDate=].

In my interface, I can add multiple lists and in each list, I have multiple documents. This is my requirement. 

a!gridLayout(
                          label:"",
                          headerCells:{
                            a!gridLayoutHeaderCell(label:"Upload"),
                            a!gridLayoutHeaderCell(label:"DocDescription"),
                            a!gridLayoutHeaderCell(label:" ")
                          },
                          columnConfigs:{},
                          rows:{
                            a!forEach(
                              items:{
                                if(
                                  ri!isReadOnly,
                                  ri!Document,
                                  if(rule!FCO_isNullOrBlank(ri!Document),
                                  null(),
                                  ri!Document[wherecontains(local!mappingId,ri!Document.mappingKey)]
                                  )),},

 

                                expression:a!gridRowLayout(
                                  contents:{
                                    a!fileUploadField(
                                      label:"Upload Document",
                                      target:cons!SHA_FOLDER,
                                      maxSelections:1, 
                                      value:index(local!Doc,"appianDocId",null),
                                      saveInto:fv!item.appianDocId,
                                      required: true(),
                                      requiredMessage:"Please upload document",
                                     disabled:ri!isReadOnly

 

                                    ),
                                    a!textField(
                                      label:"docdescription",
                                      placeholder:"enter doc description",
                                      value:index(local!Doc,"docDescription",null),
                                      
                                      saveInto:fv!item.docDescription,
                                      required: true(),
                                      readOnly:ri!isReadOnly

 

                                    ),
                                    a!richTextDisplayField(
                                      labelPosition: "",
                                      value: {
                                        a!richTextIcon(
                                          icon:"trash-o",
                                          link: a!dynamicLink(
                                            value:fv!index,
                                            saveInto:a!save(ri!Document,remove(ri!Document,fv!index))

 

                                          ),
                                          color:"NEGATIVE",
                                          size:"STANDARD"
                                        )
                                      }

 

                                    )

 

                                  }
                                )
                            )
                          },
                          selectionValue:ri!Document,
                          selectionSaveInto:ri!Document,
                          selectable: {},
                          selectionRequired:false,
                          selectionDisabled:{},
                          addRowLink:a!dynamicLink(
                            label: "Upload New File",
                            value:true(),
                            saveInto:{
                              
                              a!save(
                                ri!Document,
                                append(
                                  ri!Document,
                                  a!forEach(
                                    index(reverse({save!value}),1),
                                    'type!{urn:com:appian:types:SHA}SHA_document'(
                                      mappingKey: local!mappingId
                                    )))),
                                    local!Doc

 

                            }
                          ),
                          validations: {},
                          shadeAlternateRows:true
                        )

So when I am trying to upload a document I am unable to save it it throws me the above error! 

Can anyone please help me with this error!