Error "The given key was not present in the dictionary" When Creating New Custom Entity on Update Event - plugins

Question

On CRM 2013 on-premise, I'm trying to write a plugin that triggers when an update is made to a field on Quote. The plugin then creates a new custom entity "new_contract".
My plugin is successfully triggered when the update to that field is made. However I keep getting an error message "The given key was not present in the dictionary" when trying to create the new custom entity.
I'm using a "PostImage" in this code. I confirm that it's registered using the same name in Plugin Registration.
Here is the code
var targetEntity = context.GetParameterCollection<Entity>
(context.InputParameters, "Target");
if (targetEntity == null)
{throw new InvalidPluginExecutionException(OperationStatus.Failed,
"Target Entity cannot be null")}
var postImage = context.PostEntityImages["PostImage"];
if (postImage == null)
{throw new InvalidPluginExecutionException(OperationStatus.Failed,
"Post Image is required");}
var quote = context.GenerateCompositeEntity(targetEntity, postImage);
//throw new InvalidPluginExecutionException(OperationStatus.Failed, "Update is captured");
//Guid QuoteId = (Guid)quote.Attributes["quoteid"];
var serviceFactory = (IOrganizationServiceFactory)serviceProvider
.GetService(typeof(IOrganizationServiceFactory));
var service = serviceFactory.CreateOrganizationService(context.UserId);
var contractEntity = new Entity();
contractEntity = new Entity("new_contract");
if (quote.Attributes.Contains("portfolio"))
{
var quotePortfolio = (EntityReference)quote.Attributes["new_portfolio];
contractEntity[Schema.new_contract.PortfolioName] =
new EntityReference(quotePortfolio.LogicalName, quotePortfolio.Id);
}
if (quote.Attributes.Contains(Schema.Quote.QuoteName))
{
var quoteName = (string)quote.Attributes["name"];
contractEntity[Schema.new_contract.contractName] = quoteName;
}
var contractId = service.Create(contractEntity);

Answer 1

I think context does not contain "PostImage" attribute.You should check context to see whether it contains the attribute before getting the data.

Answer 2

Looking at this line in your post above:
var service = serviceFactory.CreateOrganizationService(context.UserId);
I am deducing that the type of your context variable is LocalPluginContext (since this contains the UserId value) which does not expose the images (as another answer states).
To access the images, you need to get to the Plugin Execution Context:
IPluginExecutionContext pluginContext = context.PluginExecutionContext;
Entity postImage = null;
if (pluginContext.PostEntityImages != null && pluginContext.PostEntityImages.Contains("PostImage))
{
postImage = pluginContext.PostEntityImages["PostImage"];
}

Answer 3

In the below code segment, you are checking for the attribute "portfolio" and using "new_portfolio". Can you correct that and let us know whether that worked.
if (quote.Attributes.Contains("portfolio"))
{
var quotePortfolio = (EntityReference)quote.Attributes["new_portfolio];
contractEntity[Schema.new_contract.PortfolioName] = new EntityReference(quotePortfolio.LogicalName, quotePortfolio.Id);
}

Answer 4

First, you don't say what line is throwing the exception. Put in the VS debugger and find the line that is throwing the exception.
I did see that you are trying to read from a dictionary here without first checking if the dictionary contains the key, that can be the source of this exception.
var postImage = context.PostEntityImages["PostImage"];
if (postImage == null)
throw new InvalidPluginExecutionException(OperationStatus.Failed,
"Post Image is required");
Try this:
if(!context.PostEntityImages.Contains("PostImage") ||
context.PostEntityImages["PostImage"] == null)
InvalidPluginExecutionException(OperationStatus.Failed, "Post Image is required");
var postImage = context.PostEntityImages["PostImage"];
Although, I don't think that a PostEntityImage Value will ever be null, if it passes the Contains test you don't really need the null check.