added missing library

SOL003/VNFPerformanceManagement-API/IndividualPmJob.robot

@@ -4,6 +4,7 @@ Library           JSONSchemaLibrary    schemas/
 Resource          environment/variables.txt    # Generic Parameters
 Library           JSONLibrary
 Library           REST    ${VNFM_SCHEMA}://${VNFM_HOST}:${VNFM_PORT}    ssl_verify=false
+Library           String
 
 *** Test Cases ***
 GET individual VNF Performance Job
@@ -118,7 +119,7 @@ PATCH Individual VNF Performance Job - Unprocessable Entity
     ...    Reference: Clause 6.4.3.3.4 - ETSI GS NFV-SOL 003 [1] v3.3.1
     ...    Config ID: Config_prod_VNFM
     ...    Applicability: none
-    ...    Post-Conditions: 
+    ...    Post-Conditions: none
     Send Patch request for individual VNF Performance Job with unprocessable entity
     Check HTTP Response Status Code Is    422
     Check HTTP Response Body Json Schema Is    ProblemDetails